GM's got a bulletin for replacement of the Pulse Width Modulated Pressure Control Solenoid (or PWM PCS) on the 4t65e for any kind of crazy shiftying, harsh, or lazy. GM part# 10478146, I think, and it seems to work. gotta drop the engine/cradle assy enough to open the side cover on the drivers side, then I'm not sure which one exactly, but its on the side of the valve body. You'll need that and about 1L of dexronIII