Lifters clacking support no oil pressure, doubt it's the gauge.
Doesn't really matter if it's a clogged pick up or the oil pump. Your gonna have to drop the pan.
If it's is a clogged pick, question is what clogged it? Hopefully it's not the nylon teeth of a silent timing chain setup. You mention it's a truck (no real details there BTW) dunno if trucks got that setup or not, but who knows what someone might have put in there.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
