My 86 blazer drives for about ten minutes in 2 wheel drive then loses power to the wheels. Grinding noise coming from under hood. Put the truck in 4 low and grinding stops and truck will move. Then I can put it back into 2 wheel and it will run great for a few miles, then it happens again. Any idea what's going on? Just had the 700r4 transmission and 208 transfer case rebuilt a couple weeks ago. Truck ran great for about a week after I got it back....

 

Did you flush the transmission cooler in the radiator. does it even have a cooler hooked up? Did you have a new torque converter built? If you did not do or have these things done then debris and metal bits could make their way into your nice newly rebuilt transmission and put you back to square one.