I have the FSUIPC and I understand that you can't have two commands on the same button/keys. I've tried all kinds of combinations with no luck. I made sure things were deleted in FSUIPC and used the trigger button in FSX FOR SLEW ON/OFF, when I go in FSX and pull the trigger the plane pitches over into the ground.I've tried the reverse and deleted the FSX control and used the FSUIPC with no luck. Once again a simple thing and a big problem for me. I've also used key presses. Any ideas?

All I've done is map my joystick axis for forward/aft and side-to-side slewing. From memory there is a 'slew' axis assignment which only works when FSX is in slew mode.

It certainly works because I have the joystick working normally when flying and am able to slew easily when in slew mode.