1993 GMC Sierra C1500 5.7 just recently started having the oil pressure drop. We think it may the oil pressure gauge where would that be at. We don't want to change the pump if changing the gauge will fix it.

Most likely the Gage is not the problem these rarely go out. If the pressure is only dropping then the oil pump is getting weaker or is filling with sludge. Try running the engine with an oil additive such as marvel mystery oil or sea-foam. Then after the additive has circulated through the engine for a few heat ups and cool downs you can change your oil. the pressure should change almost immediately. If it doesn't then check the oil pressure switch. You can look on the side of the block and there will be a small piece shaped like a pencil with a wire coming from it. This piece is the oil pressure switch. Hope this helps. Please rate me if you think this helped. Good luck.