The OP stated he's buying a 2014 Ventana LE 3845. Here's the specs for that coach from Newmar's webpage:
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Here's what those numbers mean:
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So, given all that, it appears the OP can carry up to 4900 lbs in his coach which would include the tongue weight of the towed vehicle. That said, he still should not exceed the total weight of 33,000 lbs which would include the total weight of the RV and towed vehicle. Given the above, my calculations agree with the OP's. 6900-4300=2600. However, that's assuming the dealer has not added anything to the base vehicle. The coach should be weighed ready for camping then subtract that number from 33,000 and you'll know if your truck it too heavy. Stay within the specs and you'll have no warranty issues, going outside those parameters could bring you grief.
Remember when towing, the maximum load cannot exceed the weakest link in the system whether that be the drive train, hitch rating or other factors.....Dennis