It sounds like a bad pump to me if you are taking those readings directly off the main line to the pump. I think it could be causing your shifting problems. If you have a diaphragm pump, rebuilding it is pretty easy. Took me less than an hour and a half to do it. No need to pull the radiator or the whole pump. Just remove the front of the pump with the diaphragm and check valves. Do you have a vent line going from the pump to the either the intake manifold or air cleaner? If so, check to see if it has oil in it. If it does, diaphragm is torn.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13