Q&A

 Master

A "chip" generally controls the shift points of a transmission for better power or economy. When was the transmission last serviced. Perhaps it would be best to have the transmission oil and filter changed and perhaps if compatible use a transmission oil additive called Lubegaurd (it lowers transmission temperature basically a friction modifier). If your Pontiac doesn't have a transmission cooler it may be possible to add an oil cooler or even add a larger oil cooler to lower the running temperature of the transmission. We tow a trailer and added an oil larger transmission oil cooler to our van definitely helps.

I had this problem on my '01 Montana. The actual issue was a pressure control solenoid. There are actually two of them. When the solenoid is failing it will casue the harsh shifts due to it thinkning that the pressure is low - so it pumps more through. It keeps doing this until it hits a upper limit and then just basically shuts off, giving you the harsh shifts. If left for too long only a complete rebuild can solve the problem, but make sure you get new solenoids. My '01 shifts great now that I had the rebuild done.