GM Transmission Intermittent Hard Shifting, Clunking, Jerking

GM 4T65E - 4 speed automatic transmissions found in many
1997 and newer vehicles equipped with the 3800 engine and
most 2000 and newer vehicles with the 3400 and 3500 engines.

Description:
Everything is fine when you just started engine. (It’s just fine when cold)
Sometimes after a long drive, stop and go traffic, or when accelerate really fast. All of the sudden you’ll notice"hard shifts"where car slightly jerks when it shifts. Shutting off the car for few (10 minutes) will make this condition go away until you drive a few more miles or the vehicle warms up and the hard shifting will return. (Notice Check Engine light remains OFF)

This is perhaps one of the most common problems with this transmission.
It has been a problem since the release in 1997 and can happen for no reason
at all, even with clean fluid and very low mileage.

Solution:
Replacing Pressure Control SolenoidorEPC will most likely correct this condition and again is probably the most common problem found in any year of this transmission.

Details:
The EPC solenoid controls line pressure and has a spool valve which oscillates back and forth to regulate transmission line pressure based on commanded pcm signals dependant on lots of various inputsfrom the vehicle. The spool valve in the solenoid will bind up and cause loss of pressure control from the pcm. The pcm constantly monitors shift timing in milliseconds and if this is not within programmed parameters after a few shift cycles the pcm triggers trouble code P1811 which is Max Adapt/Long Shift. This code will not set theEngine light but will dissable all adaptive shifts and will max out line pressure in the transmission which causes the harsh shifts...

Other solution is using premium engine oil to keep systems running cooler.
I have 2000 Oldsmobile Intrigue with 155.000 Kmwhen it started happening.
Valvoline engine oil worked-out as an alternative solution to replacing EPC
or Electronic Pressure Control Solenoid.