Yeah, I have had the same problem with my Shadow 1000 since I bought it over a year ago.
The very last thing I checked was how well the barrel was choked, if at all. I found that every single brand of pellet, when pushed through the breech to the muzzle, felt tight at the beginning and quite loose as it neared the muzzle.
Maybe you could do the same and post your results?
Cheers!
PS: That sticky tape on the rings really do help stop scope creep, well, it'll stop the scope body from creeping back in the rings themselves. If the rings aren't tightly enough secured to the dovetail, the entire scope/ring assembly will walk its way back to the butt of the rifle. The stop pin provided really helps there.