I have a 2001 s10 4.3l 4x4 automatic just bought it with a bad tranny I replaced it but now the drive shaft seems to "lock up" for a split second at speeds between 40 and 60 mph in 2wd. I blew a u joint apart and had them both replaced at the shop and it still making the same noise anyone have any ideas

 

Try putting grease in the yoke. This has always worked for me.