I have a 2005 Impala with about 106,000 miles.Purchased the car about 9 months ago. It has always shifted smoothly until 3 days ago.
It started shifting very hard one night. The next morning, it was shifting smoothly and has been smooth for the last two days. Any suggestions? Should I have the transmission fluid changed? I checked the fluid level. It was fine.

Thanks.

 

What type of engine do are you running?

 

Your going to encounter codes P1811, or and P0741. Hard shifts and soft long shift, I have a few friends who ran into that same problem. Your losing fluid pressure which you could have a clogged or dirty filter and could try replacing the filter and fluid. What all people always say but that is just a temporary fix. I would start there but your looking at a bad solenoid sticking or about to be stuck off your Valve body side and or the accumulator and manual servo underneath in the pan, the springs and pistons are starting to get wear causing the hard shifting as well. Most people I know have tried installing the shift kits to firm up the shifting. I haven't ever tried that but from the people I do know they all said it was worth the 50 dollars for the kit to install it and it seemed to fix the problem. There in they also had the solenoids replaced and the transmission rebuilt so could of been a nicer transmission as well that fixed the problem.

 

Your transmission is the 4T65E transmission which was a very common transmission used in about like over 50 percent of the vehicles GM made. I think it is garbage as it took them about 11 years to perfect and has been upgraded many times up to 2009. I have the same transmission on my Monte Carlo and had the same problem around 72k miles and since I have the equipment I just dropped it fixed most the parts I seen that were bad and put it back in. Right now dropped it again around 102k miles just plan to upgrade it to the HD type model as the people I have talked to said it was well worth the money and it took care of every problem they encountered down the road. One guy I know has had his in for about 51k miles now and tells me it still runs like new and hasn't had a problem yet. My sell was the new chains they made for the driven sprocket. Then the Delphi part they use for the boost valve is a long nicer as it comes with a different tipped end over the old OEM one.

 

I would start though with just replacing the filter and fluid. That is only a temporary fix though as I know your going to run into a big head ache down the road from experience with that transmission. Your PCS (Pressure control solenoid) off the valve body side is likely to fail in time if your already encountering that problem. The solenoids on the valve body side are not hard to get to though and you can get a kit for around 80 dollars and replace all the solenoids on that side.