no overdrive

we have a 94 s10 blazer 4.3 with od transmission.4l60E the old tranny went out 3&4 slipping nothing there. needed it for son back and forth to school. picked one up at salvage yard, put it and {mistake} origanal converter back in. shifts fine 1-2 2-3 but won't go into od. is it controled by computer, vacumn, and how can I check it. no ses light at 65 it should have shifted already no luck

It is all computer controlled.
It will need to be put on a transmission capable scanner to pinpoint the problem.
It could be electrical or a internal problem.
A good scanner will point you in the right direction.
Good luck and let us know how it goes.
MT