Welcome to the forum,,,, nice to have you with us. The realtree hunter has the same powerplant as the GAMO Shadow, 220, 440 and 890, etc. I have an 890 and 3 Shadows and they are all great shooters with good power. As the others have told you the rifle will definitely benefit from a tune but at the very least do yourself a favor and order a trigger from Charlie (Bob). The trigger will transform your rifle into a new shooter
As for the scope slipping (creeping). If it's moving then the mounts aren't holding, which is a common problem. Do yourself a favor and get yourself an Accushot one piece mount (either high or medium height, whichever you prefer) and remount the scope. Your scope problems will be gone. Just make sure to clean the rifle receiver, dovetail grooves and all the mounting hardware for the scope with denatured alcohol first,,,, including the mount locking screws. Clean EVERYTHING with the denatured alcohol !!!!!!!! Then use blue loc-tite on the mount base screws and let it set and cure for 24 hours before shooting. Your scope creep will be gone.
Again, welcome,,,,, I'll be looking forward to your future posts..........
Jeff