Transmission slipping - Pontiac 2000 Grand Am

We own, my wife use most of the time, a 2000 Pontiac Grand AM, large 6 cylinder, with 113,366 miles, that’s on the transmission, not the wife. The transmission slips between 65 to 70 mph. We have had the car checked for this a number of times at the dealers. No fluid leaks, all fluids changed as per owner?s manual. We have changed engine modules, all fluids including the transmission, spark plugs. The dealer shows nothing on diagnostic. I don’t see any like sparks on the in dark check, Engine runs great. No water in gas filter. I have been told it is not being caused by slipping from gear shift in transmission, not sure I believe that. Vacuum checks ok. My guess even if dealers says no I believe it’s the transmission but with the newer cars tying into the computer I cannot be sure, but 113, 366 female miles (meaning my wife some woman are great drivers and mechanics) driven miles, the other thing could be the computer or still an engine module. Drive line seems to be ok. Do any of you have other ideas? I am going to have a friend, who is a certified mechanic do another fluid change, some folks even dealers forget about the torque converter. Any help!

You most likely have a transmission that has begun to fail. It’s the slipping. Once you have a situation in which the fluid is at the correct level and any gear fails to maintain speed, you have to think that the transmission is going. I would stop spending money on fluid changes and vacuum checks and start putting money aside to replace either the vehicle or the part.

With a 2000 Grand Am, if the trans is slipping you shoult have a/ some diagnostic codes. Have it scanned.

I think that given some of the things you’ve mentioned as info, it would be good to describe what you mean by “slipping.” Exactly what does the car do between 65-70?

Slipping, engine RPM does not show a change, the car speed drops and the car jerks backward then is ok at the 65 mph rhen jerks back again after 30 seconds to 60 seconds.
Thanks and Thanks to all that offered me help.

Something like this can be very difficult and sometimes near impossible to track down.
It’s often thought that any problem will show up as a code on the computer but that is not always the case. It’s quite possible, and often happens, that an engine may have an erratic running problem or the transmission may go stupid now and then while never leaving a code.

I’ve got a few possibilities I could throw out but they’re all pretty much wild guesses.
Any chance this is a fuel delivery problem related to a clogged fuel filter? When if ever was the filter last changed?

This could possibly lead to a weak fuel pump problem.
There are a few more possibilities but I’ll dwell on that a bit.

When a transmission slips, the RPM’s rise without the car accelerating like you’d expect. What you’re describing sounds more like a cylinder (or three) misfiring, or the whole engine momentarily stalling. I’d start poking around the engine bay again rather than the transmission. What you’re describing could be caused by sticky injectors or spark failure (remember, just because the plugs are new doesn’t mean you have good spark. You still have wires and the coil/ignitor to think about).

Another good place to check is the distributor cap. If it’s cracked and the air is humid or it’s snowing/raining, moisture can get in there and cause issues.

I agree with Shadowfax and ok4450 that this driveability problem is much more likely to be engine-related than transmission related. As Shadowfax pointed out, the best evidence is that the tachometer does not register an increase in RPMs when this “slipping” takes place.

I think that OK4450 is on the right track with suspecting poor fuel delivery, and as a result, replacing the fuel filter is a good idea, even though that will not resurrect a failing fuel pump. If the OP has not replaced the fuel filter in the past 3 years or so, this could have damaged the fuel pump by making it work harder to try to push gas through a partially constricted fuel filter.

KirknDee Here, Thanks for all the responses! I hope I can help someone else in the future. I haven’t had a chance to go after the transmission problem due to the holidays and our daugther using the car and not living at home. I will keep you updated as I check out your ideas.
Again Thanks, Kirk Peel, Chief Engineer, US Merchant Marines