i have the same problem, will not shift from 2nd to 3rd without high rpm’s
A little more info would help, engine and transmission information?
thought I had. it is a 1996 gmc sierra, 5.7 4x4, automatic
OK, 4L60E? Probably.
If it actually does go into 3rd gear and stay there after the high RPM shift. I would look at the o-rings on the shift servo. And possibly the electronic shift solenoids.