Revolution 500E with APM - ALTHOLD/LOITER Problems

Hi there ,

hopefully s.o. can help me !
I have a pretty nice flying Revolution 500E wit APM 2.8 , ext. Compass and GPS.
The copter is flying okay in Stabilize and acro mode .
But if i Change to ALthold or loiter the copter is sluggish - swinging left and right when I roll- same behavior in when pitching.
If I switch back to STAB - all is fine again .
I did so many tunings on my copters- but I cannot find the problem here with the traditional Helicopter.
Perhaps s.o. can help me ???
regards ,

ACDC