The airplane was approximately 48 pounds over maximum gross weight and the runway upslope was about 1/2 degree. Takeoff ground roll for 0 and 1 degree up was 1,075 and 1,214 ft respectively. Witnesses observed initial rotation attempted after approximately 800 ft of roll. They also reported that the nose rose off of and went back down to the runway 2 or 3 times before the airplane became airborne at the end. Terrain descended at the end of the runway and the airplane roughly descended parallel to that downslope in ground effect to initial tree impact 390 feet later at 10 ft AGL. The airplane came to rest and was consumed by fire 561 ft from runway end. Although witnesses felt engine performance and acceleration were not optimum, no discrepancies were discovered. Most of the pilot's experience was in high performance USAF jets. He had 1 hour of dual in make and model prior to the accident and 3 known dual flights in civilian airplanes. The only runway used during this training was the 8,000 ft long.