I have a 2005 3.4 Chevy Impala. I've began to notice on Longer drives that it shifts hard from 1st-2nd. If I shut the car off the problem stops. I have 63,000 Miles on the car and had the trans fluid changed with a pan drop and filter at 59,000. No trouble codes, no check engine lights. Any ideas, could it be my coolent running warm? Should I get a full flush to remove as much fluid as possible? Any comments are helpful.

Adam

SPG358 and Billboost are our transmission experts, and they should be able to give you an better explanation than I can. I'm not a transmission guy, but the way I understand it as your transmission starts to slip and shifts take longer, the transmission detects this condition and increases pressure. This results in the hard shifts. I corrected this problem on my car by installing a shift kit in the accumulator. The shift kit causes the transmission to shift more crisply and the hard shifts tend to go away. At least they did on my car.

At this point, Billboost will generally chime in and tell me my explanation isn't entirely correct, but he will probably agree with the shift kit.

Oh, and by the way, the trouble codes that will be created by the problems you are having cannot be read by a standard code reader. Take your car to a transmission shop and they will have a scanner that can read transmission related codes.

I always like to add that DEXRON VI is the latest AT fluid by GM and most users report great results after upgrading to it. I had major tranny problems at 90k miles, and did the shift kit and DEXRON VI update, and I am now at 160k miles and no transmission work done.

DEXRON VI is expensive and most transmission shops do not use it because of the cost. Wal-Mart sells it at the lowest price where I live, almost $2 less a quart than the chain auto parts stores.

I too am having the same problem as you Adam. I have the same year and exact same problems as you. But mine shifts hard sometimes from a stop,like its starting in the wrong gear.been doing this for 2 years now,has 75,000 miles now.I switched over to dex 6,helped alittle.sometimes won't do it for days.VERY ANNOYING...took to trans shop no codes.hopefully will both come up with an answer

If you are sure that you actually have no codes (this problem usually sets a P1811) I would hook a scan tool up to it an monitor things like TPS, MAF and pressure control solenoid to see if it is being commanded to do what it is doing.

sgp358 lots of problems with previous years pressure control solenoid.could that be possible

Possibly. The Pressure Control Solenoid has been a major problem with the 4T65-E since it was introduced.
If you hook up a pressure gauge and scan tool, it will help to pinpoint the problem.

Pressure control solenoid was sticking open. Problem being fixed this week. Any other suggestions before I take it in for the work?

Very common problem on the 4T65E, I've changed a lot of pressure control solenoids on those transmissions for that problem. Also clean the valve body out really good.