According to the pilot's report, he leveled the airplane about 11,000 feet and established a speed of 80 mph with 10 degrees of flaps extended. When the last skydiver exited the airplane, its nose pitched up. The pilot pushed forwarded on the control wheel and added full engine power. He experienced "difficulties" in pushing the control wheel forward and thought a parachute caused the control issue. The pilot subsequently used full nose down trim to assist his control of the airplane. A witness in a chase airplane confirmed the bent right horizontal stabilizer. The pilot assessed the deteriorating flight control situation. He decided to jump out of the airplane over farmland and use his emergency parachute there. The pilot observed the accident airplane spiral down as he descended under his parachute. A skydiver reported there were no mechanical malfunctions up to the time he exited and the last skydiver confirmed that his reserve canopy had deployed prematurely as he was leaving the step. The pilot reported no other mechanical malfunctions or failures with the airplane that would have precluded normal operation.