SOME SHOPS DO CONVERT ,ON YOUR TRUCK IT WOULD BE REALTIVELY EASY AS GM MAKES THE R4 COMPRESSOR AND IS R134 COMPATIBLE CONFIGURATION , IT LOOKS IDENTICAL TO THE R12 COMP. , R12 IS PRETTY EXP TO RECHARGE A SYSTEM WITH , IF EVERYTHING ELSE IS WORKING OK, I WOULD LEAVE IT R 12 IT WORKS MUCH BETTER THAN 134 SYSTEMS, JERRY