Savage x with a f4.6 looses torque after a few minutes of running

[andu]

Engine has plenty of pinch, no airleaks that i'm aware of, slipper is tight, engine isnt overheating. Once warmed up its a wheelie monster,but after a couple of minutes wont even pop a small wheelie, tune doesnt seem to change. Running os8 plug, tried multiple different ones, but the issue persisted, honestly I'm stuck, never had such a problem. Only cause i could think of is an overheating clutch, clutchbell gets quite hot, but not hot enough to start overheating imo and clutchshoes have been ran only for like 5 tanks of fuel.