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Transmission problem? HELP!

My '99 Buick Park Avenue is awesome! But lately (last year or so–oh! it has 190000+ miles on it…yea!) after I’ve been driving very slowly (2-7mph or so probably) for 10-20 minutes - like in bumper-to-bumper traffic on the Interstate…or slowly through nearby neighborhoods to see new developments (being a Realtor…that’s what I do occasionally!)…it starts to shift VERY hard. From first to second CLUNK, from second to third CLUNK. Feels AWFUL! But if I accelerate to ‘normal’ speeds the shifting is much better…smooth as usual. Can anybody tell me whazzzuppp? And if this is fixable/normal/how to avoid?..of course OTHER than not driving slowly in bumper-to-bumper traffic…:wink: This doesn’t happen in my normal daily commute which is: from home, thru my neighborhood at 25mph to a boulevard at 42-45mph, then interstate at 70mph to local feeder streets at 30-45mph to work. Shifting is very smooth UNLESS I happen to have this very slow/pokey driving as described above. I had the transmission flushed and filters changed within the last 4-5000 miles.

Thanks ANYBODY who can help me!

Shortly, after this problem shows up have the transmission computer scanned for codes by a transmission technician. Your problem sounds like it could be the computer detecting a fault and commanding full line pressure. It is also possible that something about slow driving is causing the pressure modulating solenoid to default to fail safe full pressure. You could also have the transmission tech do a line pressure check to see if there is a pump problem or internal leakage situation. It would be nice for the tech to have the gauge on the transmission when the problem occurs, so you may have to drive around with him in the car doing the type of driving where you have seen the problem.

Hope that helps. If you resolve this problem, respond with feedback to let us know what really was wrong.