One the problems with the RV industry, is expense and price! They make units with just the minimum of everything on them. 1500# to 2500# is the window they use for the things you can put in any unit. You can order anything you want and they will put it on the unit, but it has to come from the factory. You can change your axles to 6000#, 7000#, or 8000#. BUT, that does NOT change what the manufacture states as the total weight. That is on the decal on your unit, your title, registration, etc. If you have an accident and they would weight your unit, if you are over the manufacturer specified weight, you are at fault, no matter what happened. Or if DOT stops you, as a vehicle on the road they can, if you are over the manufacturer weight you could be ticketed. We had 7000# axles and changed to 8000#, then went with MOR/ryde IS system. That's how I know, we tried to change ours, takes almost an act of congress, and you know they don't do anything anyway, so it may never get done. LOL Anyway hope this helps.
God bless,
Mike