Originally Posted by grizz1

It may well be an air leak via any of the following:

loose head bolt
loose pinch bolt screw
leaking needle O Ring
leaking front bearing (highly possible)
leaking back plate O Ring

I know you have already checked the tank and lines, but some tanks can be a pain. Have you tried a different brand of tank ??

Unless you have the top end too lean, bog below half a tank normally points to something external, other than tuning.

Have you tried running it a little rich on top then seeing if it still bogs below half a tank ?

Not trying to make you feel bad inferno, but I think it is a tuning issue
If your new to nitro motors finding the right balance can be tricky. It a steep learning curve, and we have all struggled at some stage to master the dark art