Yeah it is probably the gauge. Are all the others stable and read correct? Typical wrangler issue. You may have to pull instrument cluster and clean the cooper film everything is connected to on back. 6 screws one plug whole thing comes out. Tear down on a table and clean the contacts for all. Takes about an hour.
After that check you amp gauge and see how it reads.
89 2.5 TBI, 4" RC lift, 1" Booms, SYE, Adams Driveshafts front and rear, Ford 8.8 with 4:88s, BFG 33X12.50X15, and a ton of other stuff.
AF Jeep Club Tail Number 184