a/c,4x4,fuel guage

2001 suburban 1500 4x4 ....all in one week the a/c control would blow very hot like i had the heater on also tried to switch off and fan would stay on low, the 4x4 got stuck in 4-lo even though nobody switched it and my gas guage flips back and fourth to empty. unfortunatly I replaced both the a/c control panel and the 4x4 switch before I am asking now. The new panel did the same thing. The fuel guage started 3 days after I switched out these parts. truck has 95000 miles I use it for my job so it is on the road all the time. I thought maybe a relay or computer. PLEASE HELP I need some ideas before I take it back to the shop and spend another 1000. on replacing good parts. The dealer said I would need to probably change my fuel guage sensor after we replaced the other parts. that were still good.