So looking at it just from towing perspective, I tend to agree bigger is better .... but .... you don't tow a ton. A 3/4 ton is going to be taller, longer, a lot stiffer, and more money, not to mention the depreciation hit your going to take when you trade in your 1500. And if this is also your daily driver that also has to factor into the equation because you use it way more for commuting than towing.
It sounds like your main concern/complaint is sway when your going above 60. Before I'd spend the money on a new 3/4 ton I would give a serious look at the hitch, hitch setup and how the weight is distributed between the truck and trailer. At those weights it wouldn't take much to go from OK to scary. I would go through the setup/installation process again with the new trailer to make sure everything is correct with hitch angle, torsion bar angles etc, for the new trailer AND the new truck. If the dealer swapped the hitch components for you, don't assume they did it right. They may have assumed everything was good and just bolted stuff on, there's a good chance of that actually since the service department is usually under pressure to get it done as fast as possible so they're not holding up the sale. The hitch you have is a friction style sway control. If you've had it a while, the friction surfaces may have worn some and you may not getting as much sway control as you used to be when it was new. Also, you have air suspension, a friction style sway control depends on the angle of the hitch and the trailer to provide enough down pressure for the anti sway to work properly. The tongue weight of the trailer pushes on the hitch ball but its the angle of the hitch that affects the weight distribution AND sway control not the tongue weight. In your case, the air suspension may be working against you here by relieving some of that pressure when it corrects the ride height and changing the hitch angle (I am assuming the hitch was originally setup for a non-air suspension truck?) so you may need to adjust the hitch angle and/or torsion bar height to compensate. If adjusting your existing hitch doesn't help, you may also want to look at different hitch. I know that Hensley has one that they guarantee eliminates sway. I understand it's very expensive, bit its probably cheaper than trading in your one year old truck for a for a 3/4 ton. Even if you do end up buying a new truck later, the hitch will work with that too so its not like you'd be just throwing money out the window. I'm not sure how your relationship is with the RV dealer you bought the trailer from (I'm assuming you bought it new) but it wouldn't hurt to give them a call (or call a local dealer if you bought it private party) and explain the problem. They may have some suggestions that would help too. Most of these won't cost you anything, or very little, except some time. If you can get the towing experience back to a reasonable level of confidence for your 4 trips a year then at the very least it buys you some time to decide whether you need a bigger truck, smaller camper, bigger truck AND camper ... lol
FWIW
