Backfiring

1996 Ford, 7.5L, fuel injected, Banks Power Pack installed, Class A motor home, 43,000 miles. Rough start, followed by misfiring/backfiring, then all is well. Replaced plugs, distributer cap and rotor and fuel filter. Had electronic diagnostic: no codes. Had fuel pressure diagnostic: 15 pounds pressure normally when loaded, 27 pounds when unloaded, held pressure at 30 after turning engine off. Gas mileage appears to be about normal (for me) at 7 mph towing a car. Made it from Central California to Port Angeles, WA, climbing hills, etc. With the only significant problem occurring at and shortly after startup. Check engine light came on during that trip a couple of times, but went back out after only a minute or two.

Mechanics in Corning, CA, that did the diagnostic said fuel pump needs to be replaced. I elected not to have them do it at the time, because the coach was still able to travel and I was more interested in getting home than staying another day to meet their schedule.

Is their diagnosis reasonable or are there other possible causes of this problem that I should eliminate before having the gas tank lowered to replace the pump?

Thanks!