6t22v turbo, are you sure? You might mean a GT22V, which would be a VNT unit -- if that is the case I think a lot of us on here would be very interested in seeing pictures and more info on this setup! A few of us have talked from time to time about adapting a modern VNT to a D24T with an intercooler but I didn't think anyone had done it yet. Some photos and info on how it is being controlled on your truck would be very cool to see!
If it is able to push that heavy rig uphill at 75 mph, it must be making pretty good power -- not surprising if it has the turbo+IC setup that it sounds like it might have. Do you know what kind of adjustment has been done to the injection pump, like whether it's just been turned up or whether it has some kind of more serious modifications? In any case turning the fuel limiter screw (aka "smoke screw") out a little ways will probably help bring EGT under control, especially if you can see some visible smoke at WOT.
Re the oil pressure delay, I used to think that air leakage at the pickup-to-pump gasket might cause that symptom, but I have never taken apart one that was loose there, so I don't think that's it. A few of the oil pumps I have taken apart have had significant scoring on the relief piston and its bore. If the clearance there were to open up enough that air could pass easily, it would cause not just the pickup but part of the pump itself to fill with air, so that's the best guess I have about what might cause it in some motors. Unfortunately, those pumps I found scoring in all came off non-runner motors so I don't know what their behavior was. However, the relief piston is easily accessible on the front of the motor, so I guess it wouldn't be too hard to inspect on a car with the slow oil psi syndrome and compare to one that doesn't do it. Maybe will have to try that sometime -- not a perfect experiment but could be interesting.
In any case, this still doesn't ever seem to make a lot of difference in the engine's ultimate health, so I wouldn't give it too much thought. Just don't jump on the throttle until after the light goes out, or the turbo will hate you...
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