Engine/Transmission (1998.5 - 2002) Hard start and 1500 rpm limit???

[Diesel Nut]

Ok, Installed a FASS pump only in my buddies 2000 dually right after May Madness. NOw, it hard starts like crazy when hot, and he'll have it start, and not go above 2500 rpms for a short period of time. WTF? Any body got ideas? The truck is equiped with 275 rv injectors and a Van Aaken box, 135K miles, auto, 2wd. Been playing with taking the VA on and off, hard start stays, goofy 1500 rpm thing goes away with box off truck, wich is intermittant with box on. I'm confuzzled. Help me out guys. Thanks!