93 sub fuel gauge stuck on full?

Although, I would love to believe I have a never ending supply of gas, reality says otherwise.

@ 2 months ago I dropped the tank and replaced the fuel pump. All has been well and fine. Then @ 2 weeks ago, I filled up and she has dropped as low as 3/4 of a tank and thats all. Ive been watching my mileage and I can put in an easy 20-30 gallons while its sitting on 3/4 of a tank. I have noticed that when its filled, the marker thing goes way, way past the F mark. Probably @ .5 inch past it.

Is this an easy fix? Or do I just continue to monitor my mileage?

sending unit for guage --drop tank--pull pump