Ran really choppy at first and had 3/8 tank of gas. Filled it up and not a block from the pump it started spitting and backfiring. Cut off and could not start for over an hour. Purchased Sea Foam additive and the truck seemed to run smoother for about an hour. It them cut off after short test drive spitting and sputtering. Now for two days cannot get it to start. It will turn over and the fuel injection cuts on but still no full start. What could be wrong?