I would bet your belt is not jumping teeth. More likely your transmission is popping out of gear. As the shift forks wear and flex its gets worse. 3rd gear seems to be the worst culprit. I just replaced the shifting forks in mine and 3rd gear fork was bent to the point it would jump in and out of gear on normal cruising. It is a pretty easy fix to put the forks in, just take off the pulley, pull the fork shaft out, and take off the top cover to get to the forks. Around $150 in total parts from baker for the 3 forks and fork rod. I believe the forks get bent from the pressure of the gears trying to force themselves apart under heavy power. Don't go crazy on tightening the belt,..it wont help.