1994 GMC Jimmy gas guage 0n digital cluster

I had the fuel pump and sending unit replaced in late August of 2007. In January of 2008 noticed gas guage (digital) was not working. Guage would not go down. In March of 2008, had fuel pump and sending unit (ACDELCO) parts replaced again. Gas guage worked for a month or so then back to the same problem. In November 2008 it started in drop down below the half tank marking even thought we had a full tank of gas. Dec 24, 2008 go to start car, gas guage is 2 bars below half mark. Go to gas station, will only take 5 gallons. (Assume we have now a full tank), guage still reading 2 bars below half mark. Dec. 25, 2008, start the car, gas guage now show full tank. Drive 44 miles that day, gas guage doesn't move, we were six blocks from home gas guage goes down one bar, turn onto street and into alley gas guage goes down another bar. Has to use 4 wheel drive to get into garage, garage not even with alley and full of ice, guage drops back down to two bars below half way mark. Dec. 26, 2008 start car up gas guage still showing 2 bars below half mark.