Note: there is a Force and a Force HD. I believe the Force is beyond 3,500 lbs, but that needs to be verified. The Force HD and DX3 I believe is up into the 8,000 to 9,000 lb plus range, again to be verified by some specific unit numbers.
Today I looked at a Ram 2500 4x4 crew cab that had a cargo and passenger rating of 2,116 pounds on the door sticker. That rating is supposedly not reduced by the weight of the fuel. The 4x4 and crew cab reduce the ratings significantly.
Based on what bclemens has suggested, if the Isata 5, 30 ft, is around 2,500 pounds OCCC, that sounds like a reasonable match to me = combined 4,616 before reducing it by numerous factors that are of course different between the truck and the rv.
Could go to a Ram 3500 as well as the ride is the same as far as my butt could determine when I demoed both the 2500 and 3500. The ride ability was very good on the freeway, but like all trucks rougher over rough terrain, but so are the diesel pushers.
I think many owners prefer smaller and non-truck towable, but times change and for me this combination justifies some serious consideration.