The first time we had a problem we had gone to the Dr.and when we came out to start the truck it started and ran for about 15 seconds then died. It would crank but not start. About an hour later after cranking for a few it started. we had a diagnostic done on it it threw a code for crankshaft positioning sensor. We replaced it with a Napa part. As soon as the temperature outside would get above 90 degrees it would quit again. Another diagnostic and the same code came up. so thinking we got a faulty part we had it changed again. Again as soon as it got hot outside it would quit.So we talked to our mechanic and he suggested we try a Delco part that GMC vehicles will only work with Delco parts. So we ordered one. They are on nationwide backorder, so I am assuming this a problem a lot of vehicles are having. What I dont understand is why it only has a problem when the weather gets over 90 degrees. And of course we live in the cenral valley of californa and it is extremly hot in the summer. Does any of this make sense to you? Any thoughts on this problem would be extremly helpful we are just lost at this point. This truck has been such a great vehicle. Oh and btw it only has 48000 miles on it.