Not intending to add to any confusion but I put on a rebuilt IP some 3 years ago or so, and straight from the supplier, mine did and still does the exact same thing. Called up the supplier and he really didn't have any suggestions. The symptoms really show when the pump hasn't warmed up, yet but have shown up at random. I fiddled with the timing and replaced filters with no change.
Still runs fairly well so I don't know......
Mark Chapman DP member #653;
1983 K2500 6.2 Suburban, 4" lift, 35" tires, ATS turbo, Banks exhaust/intake, pyrometer, tachometer;
1986 K5 6.2 Blazer, 2" lift, 33" tires, Banks intake, pyrometer, tachometer
1963 wife, one owner, average mileage for the age but in excellent shape, a keeper
1992 daughter, low mileage, pretty, limited edition, but requires some money to maintain
1995 son, sports model, very fast & peppy, time will tell on durability and maintenance costs
"Grease is good"