Sluggish acceleration from stopped position

I recently took my truck to the mechanic for a bad transmission leak, they told me they had to replace the Oil Cooler Lines (upper and lower) and that they did a transmission service (flushed out the transmission), the leak is fixed, but as soon as I started driving, I noticed that the acceleration is very sluggish from a full stop, I can floor the pedal and there is no difference, once I get going it seems fine (though a bit high on RPM’s but not much). I also noticed some of that liquid sealant residue droplets on my windshield, similar to the type of sealant an AC place did for me to seal an AC leak, not sure if that has anything to do with this.

PS: I just did some research and apparently a Transmission Flush service could be the worst thing to do to an older transmissions, as some of the older worn automatic clutches don’t have anything to grab on to when the transmission is flushed clean. Another forum suggested that too much engine oil may be responsible for a sluggish acceleration and can damage my car… At first I thought it was an oil leak, I had just had oil service done previous to my transmission leak, so I had a full oil level but being paranoid I added 1 more qt of oil after I noticed the leak to drive it home, so it is possible I am driving with too much oil in the engine… Engine has 201k miles and its a 98 Jimmy, want to say that I didn’t have this acceleration problem before the transmission flush tho, even with the extra qt of oil.

If the transmission also has 201k miles, I hope they dropped the transmission pan before doing the flush to see if was even worth doing the service.


If you’re saying the engine revs up, with the car in Drive, and the car barely moves, then given the rest of your info, you may well need a new transmission. Up to you to decide if it’s worth it.

You can try a converter stall test and determine if the trans is on the way out.
Put the front wheels against the curb and set the park brake.
Shift the trans into LOW.
While holding the foot brake quickly try to rev the engine.
The engine should stall out around 2000 RPM; possibly less depending upon year, model, and so on.

Allow to idle for a minute and repeat in SECOND gear.

Allow to idle for a minute and repeat in DRIVE.

If the engine revs to 3000 RPM or even higher the transmission is slipping and is on the last legs.
If you do this test rev the engine quickly and back off of it. Do NOT rev and hold it or repeat the test countless times.

Re: Engine oil level. One quart too high wouldn’t likely cause the symptom you are describing, but the engine oil overfilled can damage the engine and/or cause seal leaks. Good idea asap to make sure the engine oil level is what the manufacturer says it should be, right at the “full” mark on the dipstick.

Re: Sluggish acceleration. It’s possible the shop forgot to re-connect a vacuum line or a electrical connector or something. Is the check engine light on? If the problem persists take it back to the shop, maybe they’ll spot the problem straight-away and can fix it in just a few minutes.

Thanks for the comments, all. Yes the Check Engine light is on, then again, it was on before I had it serviced. The truck has 201k miles, and I think that goes for the Transmission too. When the leak occurred, I did notice the liquid was reddish, but it did have black slabs along with the liquid that was originally leaking. The RPM’s are not terribly high when I accelerate from a stop, but definitely the take off speed is much slower than it was before, and I once tried flooring the gas pedal, the RPM’s didn’t increase that much, but it didn’t accelerate faster either… so it’s not reving the RPM’s too high, but at the same time, it’s not accelerating well… I would take a guess to say it goes from 0-30 in like 5 maybe 6 seconds, something like that, with RPM’s at 2k to 2.5k. It’s a 98 Jimmy SLE, 2wd. 6cyl 3.4L I think.

Since the check engine light is on – and has been on for some time – take it to one of those retail auto parts stores that will hook up their code reader and read out the diagnostic codes for you. Many of them provide this service gratis.

Excellent suggestion George, but I don’t know if most of them do tranny codes. It might be time for a compete download. I’m sure there will be some surprises there.

For the record, I would not be too quick to blame the shop that changed the cooling lines. Many shops can replace a leaky line but don’t do tranny work. It may be that the shop should have referred you to a tranny expert. It may be that the tranny was in serious trouble before the flush.

Driving around with a warning light illuminated and ignoring it means you have to accept responsibility when the vehicle ultimately fails. And it will. Guaranteed.