Differential

[Gerardo]

HEY GUY HOPEFULLY I CAN GET SOME FURTHER INFO FROM YOU GUYS,I HAVE A 2004 SIERRA REGULAR CAB Z71,WHEN I HIT THE 4 IT JUMPS TO AUTOMATIC 4x4 AND WHEN THAT ENGAGES AS SOON AS THE TRUCK STARTS MOVING IT JUMP LIKE IF IM HITTING THE GAS AND BRAKE ANYONE HAD THIS PROBLEM BEFORE? 

[swathdiver]

No, but you ought to have your transfer case checked out.  Get hold of a Tech-2 to test the controls and view internal trouble codes.