Brand new 4.3 TBI with very low oil pressure
 

I completely rebuilt the 4.3 in my 1993 G10 Van. It has 3 miles on it at this point and runs like a top, but only has 22 psi oil pressure at cold startup and about 5-8 psi when warm. At first I thought the gauge was bad, so I installed a mechanical gauge. It reads the same.
I used Plastigage to check my clearances when I installed the new rod & crank bearings, so I feel pretty confident that those are ok. The oil pickup tube was installed with a 3/8" clearance to the pan. I replaced the oil filter today just in case it was clogged with Vaseline or assembly lube, but my low pressure remains the same!
Does anybody have any great ideas (or past experiences) as to why my BRAND NEW 4.3 would have such dangerously low oil pressure?
Thank you to everyone in advance!

oil pump bad, clogged etc?

Thank you for responding! Im sorry it has taken me so long to get back to you. Dropping the pan & checking the oil pump/intake screen is the next step. I didn't think to check the lifters, so thank you for that.
I'll keep ya posted.