94 Blazer full size 350 at trans 4wd
 

I just bought a 94 blzr full size 350, at trans, 4wd. I had been driving it for about an hour ran fine parked it for about another hour. Started back down the road and it would get up to like 30 mph and would not shift on its own, had to let off of gas or punch it then let off b4 it would shift. Not losing any power runs great still just would like to find out whats goin on with it.. Anyone have any advice.. Thanks