THE PILOT STATED, THE ENGINE RUN-UP WAS NORMAL AND THE MIXTURE WAS LEANED AT 1700 RPM TO OBTAIN INITIAL EGT MOVEMENT OFF THE BOTTOM OF THE GUAGE. HE REPORTED TAKING OFF UPHILL ON RUNWAY 03. HE NOTED THAT THE ACCELERATION WAS SLOW, BUT ATTRIBUTED IT TO THE UPSLOPING RUNWAY AND NEAR MAXIMUM GROSS WEIGHT. ROTATION WAS AT 70 TO 75 KTS AFTER USING ABOUT 70% OF THE RUNWAY. AFTER LIFT-OFF, THE PLANE REMAINED IN GROUND EFFECT AND WOULD NOT ACCELERATE. THE PILOT RAISED THE GEAR AND TURNED TO AVOID A POWERLINE, BUT IMPACTED RISING TERRAIN AND SKIDDED TO A STOP. AN INVESTIGATION REVEALED THE DENSITY ALTITUDE WAS ABOUT 6860 FT. ACCORDING TO THE OPERATOR'S MANUAL, A NORMAL RUNWAY ROLL SHOULD HAVE BEEN ABOUT 1500 TO 1600 FT (70% OF THE RUNWAY LENGTH WAS 5862 FT.) A CHIEF MECHANIC AND A FAA INSPECTOR REPORTED THAT THE MIXTURE CONTROL WAS FOUND IN A POSITION THAT WAS TOO LEAN FOR TAKEOFF.