seem like it's ok.... you should be able to slip yet bend up a piece of paper when i goes through the gear mesh. Also i.v heard that the Trex usually takes a more powerful motor to lift it, it might just be something as simple as they miscalculated the best gear ratio and it just makes the lesser motors work a bit harder.
ok what pitch ae your blades at? if there too high that could be a problem, or, the moto is just going to run ot no matter what you do...
oh i forgot what size is the motor I'll bet it's a 380-400 brushed right?