Jeep cherokee overheating? Just got head gasket replaced!?

[BABY]

I had an issue with my Jeep cherokee overheating and water getting into my oil. This weekend I went and got head gasket replaced, new spark plugs, radiator flushed and filled, and new thermostat. . I picked it up from the shop (after paying $750!) and the engine shut off by itself! .. called the mechanic and he took it back and did something else to it (i don't remember what he said, sorry) .. today i pick it up again, and after about 15min of driving it started to over heat!!!! what the hell?? did i not just get the head gasket replaced for that reason???? .. anyway, i turned off the a/c and drove it home and it worked just fine. what could be wrong? we live in texas so we NEED the a/c on plus that is my husband's work truck. any advice will be appreciated thanks in advance!!!