First of all: That truck is suposed to have a 4L60E transmission in it from the FACTORY. NO other trans. will work. If it does have a 700R4 in it then that's why it won't shift.
cherck with the dealer i think that need syncromesh gear oil will blow the tranny
manual tranny's take gear oil not tranny fluid. you need to get all that fluid out and fill the tranny with 80/90 weight gear oil
change the fluid and filter and see what that does. It could be tranny fluid, or your tranny may be screwed.
There is a detent cable that comes from the tranny. It connects to the bottom of the throttle linkage on the carb.
Because it is in "Safe" mode.
Probably transmission valve body or clutch pack.it could be what is said above but i had the same problem and it was the gear on the end of the governer which is a round cap located on the side of the tranny easy to get to and replace with out taking the tranny out of car PS don't dent the cap in when reinstalling
Can be worn out synchronizing rings.
When was the lasttime you checked your tranny fluid? You might have fried your tranny.
transmission- 80-90w gear oil transfer case - atf tranny fluid
Worn out gear. You need a mechanic !!!!!!!!!!!!!!
My 1997 would not shift out of first gear, was 'throttle position sensor'.
means its time for a new trannsmission, and you probably put it in gear when moving .... i have an impala and if u take it out of gear when it is in motion say good bye to the tranny