I would still verify with the pressure gauge first.
1. Seen this happen from too high pressure and from negative pressure (fuel under vacuum).
2. The most common cause of ip wearing out early is improper incoming pressure, so even if it is a new ip needed- ensure the new one goes a normal 250,000 miles.
If you are not running the Fass water separator- add that in before new pump also. Not now (at least until problem is solved).
Still post pics of the throttle linkage please. That could be the whole issue.