If you have poor performance, especially from a standing start:
1) Get a separate, accurate tachometer - do not use the car's tachometer for this test.
2) Check transmission fluid level.
3) Engine must be operating properly, and developing full power.
4) Orient the car so that there will be no damage if it lurches forward.
5) Crank the engine, turn off all accessories (especially A/C), and run the engine at 2000 RPM in Park for two minutes, then allow to idle.
6) Fully apply parking brake and FIRMLY apply and hold the brakes.
7) Put the transmission in Drive, floor the throttle, and hold it for NOT MORE than five seconds while checking the max RPM level achieved.
Transmission Models A28.01/02/03/05/06/08/09/11 should show a stall speed of 2200 - 2600 RPM.
A28.04/07 should show 1650 - 2050 RPM.
A28.12/14/16/18 should show 1750 - 2150 RPM.
Adjust these speed specifications downward 125 RPM for every 1000 M of altitude.
If the stall speed is 400 - 700 RPM low, the torque converter freewheel (one-way sprag clutch) is slipping.
If the stall speed is 300 or more RPM high, the transmission is slipping.
If the stall speed is correct, but the car has limited top end speed, the torque converter freewheel is frozen.
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