Your struggle is like mine with my Air Hawk. I've been doing all the same sort of things, cleaning, changing pellets, scope adjustments, removing scope and using the open sights, tightening screws, changing grip, changing resting point and object used, using artillery hold, using a death grip hold, etc. etc. for two months. :0
Let me know if you ever get good groups. Best for me is about four out of five in a decent group with at least one flyer 3/4" away, almost never in the same direction either. More usual is a decent group of three with one bad flyer and one semi-flyer. I've been shooting in the basement with a steady temperature, no wind. In other words I have eliminated environmental variables pretty well. About the only thing that changes is barometric pressure.
I am about ready to give up on springers, this is my first I am sure there are some that are accurate, but my three pumpers are all more consistent. At my age I do not have the years to develop a proper hold technique. I shouldn't have to buy a gun and then pay extra to have a tuner put it into proper working order (Sorry Charlie).
I'll keep reading and posting too if I can manage any improvements.
Popadave in PA :0