I have a new (400 miles) GMPP Tranny and it shifts too soon. 1-2 shifts @ 10mph, 2-3 @ 20 and 3-OD @ 32-35 under part throttle. At full throttle the 1-2 & 2-3 happen at the same time right after one another. This tranny is still warrentied for 3 years from GM but It's been at the shop a number of times and they say it's supposed to shift like that. That is crap. Your not supposed to be in 3rd at 20. How do I fix it on my own?? Is there a vaccume bleeder screw I can adjust??

 

No it's not supposed to shift like that except at minimum throttle opening.

The non-electronic 700/4L60's use a Throttle Valve (TV) cable to control shift points based on throttle position. It attaches to the throttle linkage and needs correct adjustment. Perhaps it's not correctly attached in the transmission.

Who installed the trans?

 

15-18 MPH for the 1-2 shift, and 35-38 MPH for the 2-3 shift are the correct range for normal upshifts.
Is the GM unit specifically for an F-Body? F-Bodies use a governor that has lighter springs and weights in it than most other 700/4L60 transmissions. If the wrong governor (too heavy) is in it, it'll shift early.
You probably just need to adjust the TV cable, though. Look for your cable on your throttle body (It's the one coming up from the transmission). Near where it goes through the bracket, you'll see a button. Pushing that button in will allow you to adjust the cable. While pushing it in, slide your cable housing toward the firewall. This will increase pressure in the transmission, which will make it shift later, and firmer. I'd suggest marking the cable before adjusting it, just incase you lose your adjustment.
You might want to try starting from scratch, also. To do this, push the button in, and slide the cable all the way back (toward firewall) as it will go. Get in the car (with it NOT running) and push the gas pedal to the floor. The cable should ratchet out some. This adjustment will get you close. Moving the cable toward the front of the car will reduce pressure and lower shift points. Play around with it until you get the desired shift points listed above. BE AWARE that lowering pressure too much will burn the transmission up prematurely, so make sure you don't pull the cable toward the front of the car too much.

Frank
All-Trans Transmissions

 

It was installed by the dealer. This is actually the 2nd tranny in the last 6 months. (3 year warr) I also put in a new TV cable and throttle cable too. No avail. No matter what position the TV cable is in, it still shifts the same. The only thing the TV cable seems to do is change the kickdown. The shift points don't change. The tranny is supposd to be a performance build, specificly for the 93 Z28 by GM performance Parts. I used to have a 89 Z and the TV cable self adjusts. The 93 doesn't. How do I know when it is adjusted right??

 

If the TV cable doesn't change your shift points at all, you've probably got either a stuck valve, or governor problem. A stuck TV valve, TV limit valve, TV up, or TV down valve will cause a fixed upshift problem...But, a stuck TV valve will also prevent the transmission from having kickdown (detent) also.
I adjust the cable by shift timing and feel, but the point where it ratchets out after full TV should be close.
It's obvious that someone at the dealership where you had it done doesn't know much about transmissions.

Frank