Plain and simple, as stated above, no two trucks are the same. The WDH MUST be re-set for the new truck. If you're wandering all over the place, then you're taking too much weight off the rear axle and hitch.
When we got our TT (about 35ft, around 7500 lbs loaded...it's an ultra-light because I was concerned about the ratings of the Power Wagon), I made the mistake of letting the dealer set it up. The guy was talking about how he had about 1/2" squat all the way around on my truck, blah blah...
Should have been a red flag right there.
Couldn't run 60 mph without it wandering all over the place. Even with the sway bar as tight as it would go (I use the stand-alone sway bar...not a fan of the all-in-ones).
Now, I've been pulling campers for 25 years. Been around them longer than that. I made a few eyeball adjustments to the hitch...and the next time we went out, I was pulling 65mph with no sway.
The biggest problem today with trusting RV dealers is that NONE of them, or very few anyway, have scales to set hitches up or make sure you aren't overloading your tow vehicle. Every last one of them that I've ever been to is literally just winging it.