just bought a used/rebuilt engine for my truck. Bottom end is used unsure of miles. the oil pump is supposed to be new, when i start the truck it carries 50psi then gradually falls off to 5-7 psi when it comes up to temp. oil is new 10w-40 pennzoil, with a Bosch filter. Im going to change the pump. So should i change the bearings while im in their and also should i put a high volume pump in. The engine is built some and will be ran hard, just trying to get someone else's opinion