It is an unfortunate fact that many RV dealers will say nearly anything to make a sale :M
It's my opinion that the AF990 is too heavy to be carried on a 3/4 ton truck or even a 1-ton SRW with load range E tires... even if you're not towing.
I'm one of those people who hauls heavy camper with a slide on a SRW 1-ton truck... but doing this safely has meant spending a small fortune upgrading tires, wheels, and suspension components.
Since you're still shopping for a truck I would suggest that you consider a dually or budget $4-5K for upgrades.
Cheers
-Mark