ISM CM870- fuel pressure

[swenlarson]

Hi there- 2004 International 8600 with an ISM CM870.

Has a no code low power issue- hooked up fuel pressure gauge and took down the road. When driving and it run good pressure is like 160-225. When it becomes a dog fuel pressure drops to as low as 90-100. Let truck sit pressure comes back, always have to drive for a while before it messes up. Had vac guage on suction side of pump system and vacuum stays 1-2" no matter what happens. Is the pump repairable or must I replace? Any suggestions?

Thanks