That's a lot of work to do to a rifle and still not get tight groups, that's for sure. I see two possibilities here, the first one being that something is loose. It wouldn't hurt to double check all the screws on the rifle, mounts, and rings, if you haven't already done so. It's pillar bedded, so there shouldn't be a bedding problem. I would also put on another scope, one that you trust to be accurate, and see if that's the problem. At the same time, I would take that Leupold and put it on a gun of known accuracy, just to cross-check everything. Since you are able to shoot your other guns well, I assume we can figure that the nut behind the trigger has not worked loose, and eliminate that possibility. :grin:
If nothing in the rifle or the scope is loose, then the problem may be that your gun was put together by a gun assembler, rather than a gun smith. It's hard to say, without knowing the fellow's track record. The first possibility would certainly be the easiest to remedy, the second depends on how willing this guy is to back his work. Good luck, and I look forward to hearing how things go. It eases the pain that I feel when I think about the lemon Winchester that I just bought, and misery loves company. You do have about 1,700 more reasons to be miserable than me, though! :-)