FYI . . .
GM dropped the patent for Dexron 2 and its successor Dexron 3 a few years back
So you won’t be finding genuine AC Delco and/or GM Dexron 2 or 3 on the shelf anymore
If you want Dexron 2 or 3, you’ll have to settle for aftermarket
Or you can take your chances with genuine AC Delco or GM Dexron 6, which is backwards compatible, but I believe it’s overkill for this early transmission, and is significantly more expensive, anyways
OP used “valvoline max life ATF”, which covers Dexron II/III, as well as many other types.
http://content.valvoline.com/pdf/maxlife_atf.pdf
I’ve put that fluid into my Pathfinder’s transmission and steering, since it had Matic J/S on compatibility list and although old fluid seemed to be replaced by prior owner and it good condition, both transmission and steering became MUCH smoother, so I can assume OP’ vehicle struggles through dirt lifted by new synthetic fluid, not because of incompatible ATF. Considering the cost of this ATF, I would agree to posts earlier on this thread to flush it again, 1-2-3 more times to let it get contaminants out, possibly even using B12 to help it.
I can’t read all the previous posts. I don’t have all year, If you have a modulator valve. remove it and if you have trans fluid shooting out of the hole, let it. Then reinstall it and everything might be OK. I did that once and the problem then was to much fluid. Letting the fluid out brought the level down to the right height. Other than that, I don’t know transmissions that well. Mine was turbo 350.
Automatic transmissions are hydraulically operated devices, completely unlike manual transmissions. They don’t have gears that are physically moved during gear changes, they have clutches and bands that are hydraulically actuated.
Having said all that, the problem most automatic transmission run into is that the hydraulic seals and o-rings (and there are dozens and dozens of them) get hard with age and no longer effectively seal. A hydraulically operated machine that has internal hydraulic pressure leaks will not operate well, if at all. Clutches are not properly engaged because of insufficient pressure, and automatic transmission clutches cannot tolerate slipping at all, they’re very thin, not much thicker than about two business cards.
The Berrryman’s is a solvent that helps to soften and resuscitate the old hard seals, and keep an aging transmission alive for a while. It’s a crap shoot, sometimes it works well for quite a while, but if left in too long it can soften seals and o-rings so much that they’ll leak even worse. Sometimes it doesn’t help it all.
I figured that Berryman B12 might be a crap shoot. I think it probably loosened up a bit of varnish that was causing issues. Basically under light throttle such as starting out from a green light on a slight uphill, there would be a shudder and then it would clunk and be in gear. It was a Cadillac Northstar transmission in a 2001 or 2002 Deville if I remember correctly… That might matter.
I also talked to someone who suggested a capful of brake fluid in the transmission. I thought this sounded risky as brake fluid is nasty stuff.
Shudder and lurch into gear is the classic symptom of low pressure caused by leaking seals. Speeding the engine up raises the pressure and suddenly the transmission’s clutches engage, but with the engine at an elevated speed. The lurch is the standard result.
The Berryman’s softens the seals so that they seal better, for a while. Brake fluid swells the seals for pretty much the same result, although I’ve never heard of a transmission treated with brake fluid lasting very long. It used to be something to get the car off the freeway and directly to the transmission shop.
I agree with Nevada_545, your TV cable is out of adjustment. It runs from the transmission to the throttle body and controls shift points. There is a button on the throttle body end that you push in to adjust it. Move it one notch at a time until you get the shifting like you want it. Lots of videos on youtube showing the adjustment procedure.
Do additives in fresh transmission fluid work to soften seals as well? She had the entire system flushed and the filter changed at the GM dealer. The transmission seemed to shift great for the next two years or so that car was around.
The first thing I’d try is MMO - Marvels Mystery Oil. It’s sold at every auto parts supply store. Drain a small amount of tranny oil (6-8oz) then add about 6-8oz of MMO. Drive it for about 20-30 miles going through all the gears slowly so as not to force anything. See how that works and then please report back. It sounds to me that you are lacking fluids in your clutch pack. Some times it just takes going through the gears to lubricate properly.
That’s a tall order
Because the automatic transmission this vehicle has almost never came with a drain plug on the pan. VERY rarely.
Siphoning it out through the dipstick tube would work.
Sure, but it’s a lot more work, versus just loosening a drain plug
Not every DIY guy actually has a fluid evacuator/dispenser at home . . . think mityvac
Disconnecting the upper transmission fluid cooling line from the radiator and attaching a plastic hose that is hung into a container will allow starting the engine for a few seconds which will pump out a pint+ of ATF.
I had a funny experience with my 2012 Altima CVT, where I decided to change the fluid @ 60K miles.
Made a small research over Internet, mostly YouTube, from which I concluded CVT has no drain plug and decided to drain it through the filler tube.
Spoiler: I did not even check if I do indeed have a drain plug or not.
Anyway, HarborFreight has a brake bleeding vacuum pump, which I connected together with 2-quart rigid plastic can from applesause and some tubing.
It took me only 15-20 minutes to suck 5.5 quarts of fluid until I’ve got it almost dry.
Total capacity for CVT is 7 quarts, so it was not a bad result, I replenished with synthetic Valvoline CVT fluid and was very proud of myself… until on next oil change found I do have a drain plug 
My “new” daughters car is 2007 Altima, replacing CVT fluid there was way much faster, yielded tad bit under 6 quarts.
So, based on this project, I would not go “drop pan” route ever again, at least if I can get well over the half of transmission capacity through the filling tube.
If/when you do remove the pan you may find that there is a layer of sludge on the bottom. It’s the worst of what accumulates in an automatic transmission and it is a significant source of transmission problems. Of course I’m speaking from experience with conventional automatic transmissions and not CVTs.
CVT would not be very different with this regard, but I would resort to “drop pan” only if fluid change is very much overdue, as then visual inspection is really in order
having maintenance done on schedule and fluid in good state, I would not expect much need for it
my 2 cents
I have done it with a simple piece of tubing and a turkey baster to get things flowing. Very slow, but it worked.
I don’t think I’d put Marvel Mystery oil in my transmission for any reason. It appears to be a petroleum based product and even Marvel’s website says nothing at all about using it in a transmission. Petroleum based oils can whip into a froth inside a transmission, and that is something you don’t want to happen. Petroleum based stuff can do a lot of damage to seals, too.
But most of all, you do not need to lubricate your clutch pack.
And yes, transmission fluid MAY contain something to help restore the seals, that’s typically what high mileage oils and fluids are for. Sometimes they work, sometimes the hardware is just too far gone.