My 2003 gmc safari cargo van has been trying to overheat when I turn ac on what could it be?

See the pictures on the web:
images for 1996 gmc 2500 Safari van with 5.7 AC

Don't know the model but this would't be unusual on van / minivan designs.

using a test light check the fuses with the key on as some fuses are only powered when the key is on. check both sides of the fuse.

Hello and welcome to FixYa!

I strongly suggest that you replace the transmission fluid. If the fluid is burnt the transmission tends to be sluggish and finds it hard to shift gears. This will surely give great stress to the engine. Once the fluid is replaced, smooth drive and shifting will be noticeable.

Hope this helps and thank you for using FixYa! Have a good one!

whats a safari GMC?? just shows you how much i know ---- never seen one but if it fits then your ok ,sorry but very rare machines here in spain ,now ask me about a renault or a peugeot

Try waggling the steering wheel while attempting to turn the key.

DISCONNECT YOUR DRIVE SHAFT FROM THE REAREND THEN TURN YOUR REAR BY HAND AND IF YOU STILL HEAR CLICKING OR GRINDING
DETERMINE FROM SIDE OR MIDDLE. IF NOT BRAKES THEN REAREND BEARINGS. THESE REARS WERE FAMOUS FOR REAR BEARINGS.
AFTER REPAIR INSTALL SYNTHETIC FLUIDS.

you should be able to find a good fuel pump for your Safari at O'reilly Auto. Part #FE0114 for $119.99 + tax

does your starter turn the engine at all?