1990 Other Chevrolet Models oil pressure

I own a 1990 Chevy C/K 1500 2wd with a 350. when i got the truck the oil was over filled and the oil pressure gage went all the way over so i thought it was becouse there was to much oil, well i drained it out to a little bit below the full mark. the gage still went all the way over, so i dove it around to see if it made a diff. well i got to looking and when a hit the gas it goes from 60psi to 55psi. backwards? so im not really sure what to do.

thanks for your help