Go to your local Chevrolet store and get a new gage
There are 2 different gages for these trucks
0-100 ( I think)
The sending unit must match the gage
Would not hurt to get a gage and a sending unit at the same time.
Should give you another 20-30 yrs service
I had to replace both of mine in 2001-----oil pressure dropped to 0 and stayed there for about 2 weeks-----apparently not an engine issue.