The factory intank pump 'upgrade' is junk. After putting in a fuel guage in my '01, I had 12psi idling. Driving it (truck unloaded) would drop the psi significantly. At 7/8 throttle, it would be at 0. The injection pump needs to see 10psi minimum at all times. This will definitely damage/overheat an injection pump.
Pulling a trailer with your factory intank pump, I'm guessing your injection pump has possibly expired.