New 5th wheel doesn't tow well

An air ride pin box should work just fine with the Anderson Ultimate Hitch, because the Anderson adapter attaches to the PIN, which is the same regardless of whether it is a fixed pin box or an air ride pin box.

I agree that your truck may be a little light for the trailer you're towing. Those dry weights are meaningless once you've loaded up ready to camp. 1750lbs could burgeon to 2750lbs on the pin easily.