Thanks for the replies, but please read our question carefully. The oil pressure is fine at idle, but drops when pulling a grade at an RPM that is higher than idle. This does this only when the engine is cold. Therefore, it seems unlikely that it would be the gauge (which has a line to the gauge, not electric). Also, a clogged screen would seem unlikely since the pressure is fine at idle and at running speed as long as the truck is not pulling a grade. But dropping the pan and cleaning the screen might not be a bad idea in any case. The oil, non-detergent 30W, is clear.
