its been my experience on the 2-3 shift in a 4l60... the spring on the 2-3 shift valve needs changed. SLight changes make big difference in road speed - RPM shift point.
Ounces on change is all that is needed. Stiffer spring will hold off the upshift to higher road speed.
Altering the governor often affects other shifts points more than the 2-3 shift point. You get the 2-3 where you like, the other shift points are then out of whack to your liking
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