There is a TSB (Technical Service Bulletin) for what you are describing. It requires the use of GMs test equipment though to correctly diagnose it. I will send the TSB at the bottom. If you do choose to go with a rebuild or a remaufactured transmission Make sure you check the warranties out. A three year warranty is much better than a one year for the $200 difference. Make sure you check on a GM SRTA transmission. They are rebuilt by a certified rebuilder by GM and they have a very good warranty. In my experience they run close to the same price as a Jasper. With the SRTA you can have warranty work done at any GM dealership. I work in an independent garage and we sell these transmissions over all of the others.
Bulletin No.: 0O-07-30-002B
Date: July, 2002
Subject: Slips, Harsh Upshift or Garage Shifts, Launch Shudders, Flares, Erratic Shifts and Intermittent Concerns, DTC P1811 or P0748 Set (Replace Pressure Control Solenoid Valve Assembly)
Models: 1997-1999 Buick Riviera1997-2002 Buick Park Avenue1998-2002 Buick LeSabre1999-2002 Buick Regal2000-2002 Buick Century2002 Buick Rendezvous1997-2001 Chevrolet Lumina1997-2002 Chevrolet Monte Carlo1999-2002 Chevrolet Venture2000-2002 Chevrolet Impala1997-1999 Oldsmobile Eighty Eight1997-2002 Oldsmobile Silhouette1998-2002 Oldsmobile Intrigue2001-2002 Oldsmobile Aurora (3.5L)1997-2002 Pontiac Bonneville, Grand Prix1999-2002 Pontiac Transport/Montana2001-2002 Pontiac Aztekwith Hydra-Matic 4T65-E (RPOs MN3, MN7, M15, M76)
This bulletin is being revised to add additional models and model years. Please discard Corporate Bulletin Number 00-07-30-002A (Section 07 - Transmission/Transaxle).
Some owners of the above vehicles with a HydraMatic 4T65-E transaxle may comment on harsh upshifts or harsh garage shifts, soft shifts, shudders on hard acceleration, or shifts erratic. These conditions may appear intermittently or set a DTC P1811 or P0748. During diagnosis, a low or high line pressure (actual versus desired) may be observed.
The above condition may be due to any one of the following which may affect line pressure output:
Sediment inside the pressure control (PC) solenoid valve, causing the PC solenoid valve to mechanically bind.
Important: Any of the above conditions may be intermittent, therefore, this test should be performed at least three times.
Refer to the Line Pressure Check Procedure in SI, along with the Line Pressure Specification Table shown, to determine if actual versus desired pressures are within the values specified. The Scan Tool is only able to control the PC solenoid valve in PARK and NEUTRAL with the vehicle stopped. This protects the clutches from extremely high or low pressures in DRIVE or REVERSE ranges.
Refer to the Line Pressure Specification Table. The pressures in the table assume a temperature of 70°C. The pressure will vary with a change in temperature.
If the actual versus desired pressures are not within the values specified, clean the valve body and replace the PC solenoid valve, if necessary.
Check the PC solenoid valve actual versus desired pressures to verify the new PC solenoid valve is responding correctly.
Refer to the Automatic Transaxle Section of the Service Manual for the proper repair procedure.
Line Pressure Check Procedure Tools Required
J 21867 Universal Pressure Gauge Set
1. Install a Scan Tool.
2. Start the engine and set the parking brake.
7. Turn the engine OFF. Remove the oil pressure test hole plug and install the J 21867.
10. Access the PC solenoid valve control test on the Scan Tool.
11. Increase the PC solenoid as shown actual current from 0.0 to 1.0 amps in 0.1 amp increments. Allow the pressure to stabilize for five seconds after each pressure change. Read the corresponding line pressure on the J 21867.
16. Install the oil pressure test hole plug.
Tighten the oil pressure test hole plug to 12 N.m (106 lb in).