Just an update on this thread, I have been using petro ultra 94 or petro 91 fuel with no problems at all, truck has been running great. So i tried to go back to shell vpower 91 and the stumble came back right away. once i changed back to petro the stumble was gone, i can't understand how a different brand of fuel could do this. i thought if it was the fuel it would happen more than just the first start of the day. The only difference is that the shell vpower fuel around here is ethanol free.