Check the fuel pressure, my guess is that the pump is OK. Bad pump will cause truck not to run, run out of power at higher speed (fuel filter will also cause) and extended cranking. The pump is run by a switch on the oil pressure and will run until the pressure go's down. Mine has 15w 40 and will run for a long time if the oil is cold. There isn’t a shrader valve on the TB GM engines you have to unhook the line and put a T in it. If there is enough room I do it at the filter.