Help Please

2001 burb 1500 4x4. I am continuing to have problems with gas tank sensor, a/c control, and 4x4 switch. I took truck into dealer when a/c was blowing out super hot. I bought a new control panel. while truck in the shop 4x4 switch got stuck in 4-lo. bought new switch. after driving away fuel guage shows empty tank with low fuel warning light even when tank is full. this happens off and on. dealer says buy new sensor $500. installed. same week a/c blows hot again (like the heater is on). I removed the fuse and messed around with the relays and a/c worked again but it would not turn off completly. I had it switched off but air was still flowing. I pressed the resurculate button and light stays on and air stops. does anyone have a clue before the dealer charges me thousands of dollars to "rule out" the problem?