THE 57 YEAR OLD PILOT DEPARTED LATE IN THE DAY FOR A 7 TO 8 HOUR CROSS COUNTRY FLIGHT TO BEAT SOME INCOMING WEATHER. HE HAD BEEN PHEASANT HUNTING FOR TWO DAYS PRIOR. THE SECOND LEG OF HIS TRIP WAS A DARK NIGHT DEPARTURE FOR WHICH HE FILED A VFR FLIGHT PLAN AND INDICATED 12500 FEET MSL AS HIS CRUISING ALTITUDE. RADAR DATA DISCLOSED THAT HE CLIMBED TO 13100 FEET AT ONE POINT, HOWEVER, HIS OVERALL ROUTE OF FLIGHT FOR NEARLY 3 HOURS WAS ONE OF A MEANDERING AND UNDULATING TRACK. THE APPROXIMATE LAST 10 MINUTES OF FLIGHT WAS A GRADUAL ON TRACT DESCENT TO IMPACT AT ABOUT 5700 FEET, ABOUT AN HOUR SHORT OF HIS DESTINATION. HE CARRIED NO SUPPLEMENTAL OXYGEN. FRIENDS INDICATED HE FREQUENTLY TOOK 'CAT NAPS' ON LONG CROSS COUNTRY TRIPS WHILE LETTING THE AUTO PILOT FLY THE AIRCRAFT. HIS AUTOPILOT WAS OPERATIONAL EXCEPT FOR THE ALTITUDE HOLD.