What is causing my 2003 Jeep Cherokee laredo to keep shutting off while driving

When the problem is ongoing, did you do any basic testing? In that 30--40 minute wait, if it cranks good but won't start, wear gloves, have a helper crank it while you check for spark at the spark plugs and fuel injector pulse. Check fuel pressure, try not to spray gas all over a hot engine. If your missing all three have to check cam and crank sensor signals. I'd check sensor wiring circuits before replacing anything. Replacing parts parts w/0 doing any testing is not a good idea. I don't know what kind of testing/diagnostics Pepboys do? If they only check for codes, that is good as far as it goes, but, that doesn't go very far. Certainly there could be other issues, have to test when problem is ongoing.