in GM motors all the oil pumps have a pressure relief valve that opens at 70 psi give or take, and they are reliable. it's normal when engine is cold- really oil is cold- to have higher oil pressure and the higher the rpm the higher the oil pressure. as rpm increases steadily you should see oil pressure on the gauge rise steadily then stop at 70 psi. if the needle goes way past, or bounces or doesn't make sense then it's most likely the oil pressure sensor or the gauge cluster. your year falls within the gauge cluster stepper motor recall years, but if the oil pressure needle seems to make sense most of the time then i would guess oil pressure sensor being off. if you have an 8.1L, there is an NPT fitting right next to the oil filter you can undo and hook up a mechanical pressure gauge to know what's really going on. easy way to do that is remove wheel well cover.
