Hard shifting tranny in 99 pontiac

[maceman05]

My transmission started to shift hard today. I've never had a problem with it before. Always shifted good. It feels like it has a shift kit in it now. And i know this is not normal. I checked the fluid and it was full and clean, and didn't smell burnt. Any advice would be much appreaciated. It is a 1999 pontiac grand prix gt, 3.8l, automatic transmission, with 127,500 miles.

[maney8295]

pressure control solenoid most likely...happened to my '00 gt at 75k

[BNaylor]

When was the last tranny service...ATF and screen filter? Harsh upshifts only and/or downshifts? What does it do when you manually downshift each gear?

For suspected PCS issues get it scanned with a trans capable scan tool and look for a P1811 DTC (max adapt, long shift).

[maceman05]

My last tranny flush was at 100,000 miles. My wife drove it to work today and had no problems. But when I drove it yesterday when it upshifted it shifted hard. But when it down shifted no problems at all. I didn't try going through the gears manually. Tranny fluid it full and clean and no burnt smell. Thanks for the all the input.

[BNaylor]

How bad is the upshifting? Does it bang and feel like metal on metal? You may be experiencing problems as a result of the flush. Very common to see this issues pop up over a period of time after a flush. It is recommended to do a pan drop consisting of screen filter and and ATF resupply only for the 100K mile tranny service. When the hard upshifting occurs try manually downshifting and see if it feels just as bad. If any DTC like P1811 is set and stored then the PCM module commands maximum line pressure and disables shift adapts. As mentioned earlier get it scanned with a trans capable scan tool or one that can read GM extended codes. In most cases the P1811 code does not trigger the SES/CEL light but the code will be stored in history for retrieval.