2004 Chevy Avalanche erratic gauges

Computer problem
2004 Chevy Avalanche V8 Four Wheel Drive 80000 miles

Hi The first thing I noticed was that the check 4 wheel drive light came on during start up (and still does). The axles and bearings check out ok. Then a few months later the gauges would be erratic. Sometimes the oil pressure gauge will go to zero and other times it will go off the max reading. Often times the speedo will gradually start going toward the zero example at highway speeds it may show 35 mph. Is there a computer that governs all of these and if so where is it located or is it perhaps other problems? I feel that the oil pressure is ok or the engine would have suffered catostrofic failure by now. The temp seems to be ok and gauges still continues to give me fairly accurate instantanious mpg so I feel that at least part of the gauges are working properly. Is this a problem that I can handle or should I take it to a mechanic. I am comfortable working on old pre-computer type autos.