Rick:
The big difference in weights between you and Rich is that he believed he had about 500# of water aboard because he hadn't dumped his water after the PDI, and you reported only about 10# of water. That would drop his "dry" weight down to 11,400# compared to your 11,860#. You had the slide awnings--not sure if Rich did--which could account for part of the difference. You estimated they weighed 200#, which still leaves about a 300# difference when you toss in his 2d AC. At this point, 300# seems like a big thing--that could be a 2d AC plus a washer/dryer plus .... LOL LOL. Seems weird to be excited about finding 300# more of a weight allowance to use.
As for the higher GVWR that Montana put on the early 2006 3400s, since I assume they didn't change anything structurally when they dropped the pin weight to 1975# in later brochures, it just reinforces my belief that their GVWR numbers are bogus.