I did three things, and my P22 is now very reliable.
First, I lightly oiled all the mating surfaces, and then while watching TV I racked the slide very rapidly several hundred times tu burnish the contact points.
Second, I switched to hotter ammo -like mini-mags or velocitors- while I was breaking her in. More recoil seems to help cycle the action. Ironically, the first ammo that I found to work 100% was that subsonic Aguila Sniper SSS stuff, with the .22 short case and the long 66 grn bullet; I guess that the larger heavier bullet and shorter case to extract was just what my gun wanted. The only reason I didn't keep using this ammo is that it's midget case would leave fouling in the chamber where the .22 short case ended that would gum up regular .22LR rounds.
Third, I added a suppressor. With the added backpressure of a can on it, the gun cycles any ammo, even cheaper subsonic, without a hitch. Of course, if I take the can off after 500 rounds of quiet fun, the gun by itself is then a single shot till it's been cleaned. And, as a testament to it's reliablility, I took it shooting with my buddies kids the other day... the two of them shot through, no joke, about 2500 rounds of the Federal bulk pack wal-mart stuff. There was only one failure that I recall, which was a stuck case that I had to pop out with a rod.
I hope some of this helps! And here's a gratuitous pic of mine!
Edited to add: I went back and re-read that you've already had a can on yours and it didn't help at all? Wow, I would try the burnishing I did, and then use very little oil when running the gun, just enough to lube the surfaces, but not attract all the crap that's left when shooting .22