2002 GMC Sonoma 4 WHEEL DRIVE

Looks like nobody wants to jump into this, because really it could be quite a few things, lets start with the ones we hope! 1st, go to auto parts store and run your OBD, check all fuses and relays in cab and under hood, check shift linkage make sure it is not bent and is adjusted correctly, vacuum switch you hope its bad on 4hi, next Vacuum Actuator / Shift cable, Transfer case control module, check Electronic shift motor if you go through this list and cannot find problem, you may need a transfer case or? My 4x4 trouble-shooting experience has been 60% of the time electrical, 30 % Driveaxles, CV's inner and outer, transfer case, driveshafts, 10% a cross between an elephant and a rhino, GOOD LUCK!