I have a 1996 Blazer 4.3 auto 4x4. The problem is that 1st does not work after about 5 min of driving and overdrive does not work. Both stop about 5 min after the blazer is started.

 

This definitely sounds like an electrical problem, but not having 1st or 4th at the same time is a VERY odd problem and one that is not covered in my reference materials.

 

New problem now, 1st nor overdrive work at all. No matter how long it sits or cools down they do not work at all. But the others work fine, and reverise locks in better now then it ever has.

 

*subscribing* I have the same problem wih my 98, have no 1st or 4th, doesn't shift from 2nd to 3rd, check engine light, etc.

 

Check all your ground straps to your computer and tranny, etc...
You gotta find someone (a shop) who has a tech2 or equivalent type scanner to "see" whats going on.

 

i have the same exact problem no 1st or overdrive, i have another tranny ready to go but if this is a simple problem i would like to get a few more miles outta this one. keep us updated did you figure anything out