65 Barracuda daily driver

i'd throw a pressure gauge on it and see what you've got cooking before tearing into things and stuffs.

pick up clogged is a possibility. pump going bad is a possibility as well. incorrect clearance from pick up to pan is a possibility. it's unlikely that you borked anything putting it together as it wouldn't work right from the jump. so, maybe if the pick up is new you didn't get it screwed into the pump enough and it's sucking air?

more likely lifter bleed down or an issue with oil getting to the top end. what do you have cam/lifter/rocker/head wise? if it's mix-n-match you may have a compatibility issue in there somewhere.

or just the pump or drive sucks.

and yeah, you can do the pan in situ. it sucks though.