I know this is not exactly Thirdgen related (My 1997 Express), but lets say one of our readers has a LT1/LSx swap with a 4L60E in a thirdgen. I have found the line pressure in typical OE applications of the 4L60E to be annoyingly low. Even after a shift correction kit by Superior, it still shifts too soft. I ran across a Vacuum modulator kit for a 4L60E made by Transgo. They claim it works great in Heavy Duty and performance applications. Any truth to this. Basically they replace the Electronic Pressure Control solenoid with a vacuum modulator. With no vacuum the line pressure is 230-250 PSI, when vacuum is applied the pressure is reduced. The highest I have seen an OEM line pressure setting at with a 4L60E is 180-190 PSI. My 700r4 in my 1983 runs at 275 PSI @ full TV extension. I love the way it shifts, crisp, almost instant shifts.

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You can increase the line pressure in the PCM calibration.

 

The PCM cannot change the WOT pressures, just part throttle. Yes, the TransGo vacuum modulator can raise line pressure quickly. I have used them in the past successfully in certain situations, as they offer very quick downshifts. The best WOT pressures in forward gears in the 700R4's or 4L60E's is apx. 230 - 240psi., any more than this starts to get hard on the gear train splines. There are always exceptions, but this works very well from what I & other builders have seen over the years.