I have a 1988 GMC Sierra 1500 and I have issuses my oil pressure gauge is stuck all the to right and my gas gauge is stuck all way to the left and my fuses are good and i put a new fuel pump in the gas tank and it is grounded good I even put a different gauge panel in and it reads the same as the other one does.When I first tried the second gauge panel it was before I drop the gas tank i had oil pressure gauge it read about 28 pounds of pressure ,then I put the new fuel pump in the gas gauge would move all around for about one half hour then drop to empty where it is now but te oil pressure gauge lasted about a week before it when the oppisite direction to the right where is today

 

For the oil pressure gauge, I'd check the Sending Unit. On a 305/350 it is behind the distributor, kind of a PITA to get to. It is a common problem.

Gas gauge...if that sending unit went out, it is even a bigger PITA. Sorry.