Hey,
I have had quite a bit of experience with the Trx-15 pro. The truth be told it sounds like your down on compression. If the engine doesn't seal tight enough to make proper vacum as the piston travels downward it is impossible for it to suck fuel into the carburetor especially at a constant rate.

Generally when this starts to happen your truck will only use so much of a tank of gas then die, fuel won't go to the carb even if you hold you finger over the pipe, the engine becomes hard to start and may begin to hesitate.

Think back, how many gallons of fuel have you ran through this motor? Was it broken in properly? How hard a life has this motor had?

The best way to tell is to disassemble your engine (Don't get scared, its easy) Simply take the head bolts loose and pull off the head (don't loose the shims) then pull the 4 bolts out of the starter cover or back plate (don't tear the clear gasket). Then reach in and disconnect you connecting rod from the crank. At this point see if you can push your piston to the top of the sleeve or out of the sleeve, if you can do either its time to rebuild (sorry). The piston should stop about 3/16 of and inch or so before ever getting to the top of the sleeve.

I been there and know what your going through.......