If you drop it into D or OD and run it up to 4K rpms or a little more will it shift then?? Ive got that problem in my sonoma. It wont shift from 1st to 2nd until i almost hit the engines redline. If so it could be that the governor has some crap in it and it needs to be pulled out and cleaned. I just found out that is whats going on with my truck yesterday.
The guy at the tranny shop told me how to check it. Take your truck out and drive it in reverse for about a block (you dont have to dog it or go fast), stop-leave it in reverse and shut the truck off. Then put it in park and restart it. Put it in OD and drive it, see if it shifts ok then. Mine didnt at first. Then I shifted the truck manually from 1 to 2 and so on and it shifted perfectly at the correct rpms. Be warned that the problem will come back. My truck only worked right for about 2 blocks and then screwed up again. But at least now I know what needs to be done. Hope this helps you as much as it helped me.
