Hi Steve,
just got your mail and also picked up on this thread.I'm not 100% convinced this is a Mule problem as they're closer to a PAF than just about anything you can buy, B Bs in particular!
BBs do have AII but the BBPros also have AVs which can be brighter. Now as for mush, like HJM rightly says, AII is the king of mush..........I use AIV Mules in an original '70 Goldtop in the Ozzy tribute I do, obviously mush wouldn't really do in this situation :D and as the Mule clip in the demo room along with all the other guys Mule demos abley demonstrate, they're not mush monsters, far from it, they're really defined right down into the bass - clean or overdriven.
So what we need to do is get these back, let me check them again myself in one of my LPs to make sure we're all singing from the same hymn book and then proceed from there.
A brighter PAF tone would be Riff Raff with AVs or Stormy Mondays even.
I expect that the BBs you have are all sub DC8K and AII hence the slightly scooped mid and edgey highs.Into an amp eq'ed for this, ie with more bottom to roll out the highs ,the more powerful Mules will force the amp into break up alot quicker especially as you're running the master flat out.
This doesn't explain the neck tone though as the Mule neck is as open as I can wind a humbucker neck...........funnily enough the email after yours was a customer called Terry who was on a quest for the ultimate clarity from a neck humbucker and having tried all the Burstbuckers, SDs etc went for a Stormy Monday and found what he thought was unattainable-clarity in a LP neck slot!The Stormy Neck is only mariginally lower in DC than a Mule and they both have the same wire and same AIV magnet.
Whatever happens I'll get you sorted Steve so don't worry and you can always give me a call anytime if you want to go through the options. :D