Interested in your final result, and what you find had it so stuck, I suspect epoxy in my case, but have not actually had to remove it yet.

How soon does this need to come off. Send me an email and maybe I can send pictures via text or mail
you the tools to do the job. Steve (CTR)

I have tried nearly everything suggested and then some so it looks like I am going to use a small Dremel cutoff wheel.  

The ones I have seen have three allen key grub screws in them.

I use a three prong puller and a large flat washer with a small hole in center. Steve (CTR)

A cheap one from Northern or Harbor should do.

I use a puller and a small piece of flat steel (with a divot in the middle) that acts as a bridge for the puller to push against; the sleeve leaves a little edge of the filler neck exposed for the bridge to rest on.

Otherwise, how about a piece of flat steel bent into a (kinda) elongated Z shape.... One edge goes under the bottom edge of sleeve and the other somewhere to hit with a hammer.  Tap gradually around the circumference of the sleeve until it lists far enough to remove.

Cheers, Ian 

I need o take my tank out and can't get the threaded brass sleeve off the tank neck.  Heating it may not be the best idea so I am thinking about using a gear puller slide hammer combo but I hate to buy one for one use.