need engine guru advise.....high oil psi

[Old Guy with 87 GT]

my oil pressure has been goofy within the last couple of days .......figuered i'd see what you guy's could make of it

the specifics::::last week i noticed my oil pressure wasn't fluctuating like it normaly does.......was stuck at a lower pressure:like 20-30 psi.......when i took it for a good size drive and wound it up a litte the pressure went up to around 45-55 psi and stayed there........it's been staying around 50 psi ever since then............i checked the guege so it's not that(changed sending unit and varified with after market gauge)......i changed the oil filter so it's not that

this has me puzzled......the pressure is the same whether i'm taching 5,000 or at idle,whether it's cold or warm........it fluctuates a little (like from 45 to 50,55 psi) but not as much as usuall,before it would fluctuate from 10 psi to 75-80 psi depending on rpm and temp......now it just seems like the guage is stuck(even the aftermarket gauge)......the engines not runing real hot and doesn't seem to be making any funny noises.........

i'm concearned becouse the sudden change might suggest some internal problems........i just don't know what would cause it......the pump works becouse it has pressure but why isn't it dropping at idle or when the moters warm...............any insights would be appreciated .....thanks