I think the forward clutches might be welded together in my sons 700R4.
He was stuck the other day and was rocking the truck back and forth from drive to reverse trying to get out. The operationg temp got up to about 220*.
Then some smoke rolled out from under the truck and we could smell trans fluid.
After we pulled the truck out we noticed it felt like we were pulling an anchor when in reverse.
Now low gear feels sluggish and with the trans in reverse the truck won't hardly move. Like the brakes are applied. I checked all the brakes.
Any ideas?

Sounds like he burned it up !

My first equipped vehicle with a 700R4 (1990 Blazer) went with 75,000 on it. The overdrive was first to go. What kinda mileage are we talking about??

if you start it and put it in neutral and it wants to drive forward, you seized the forward clutches on. which means it needs a rebuild.