Assuming we are talking about a 5th wheel or a simple ball and only an inch or two of sag removed...no, there should be no measurable difference. There simply isn't a mechanism to change the loading on the rear axle (theoretically, centers of gravity shift but so little that you won't be able to measure it reliably).
With a weight distributing hitch...it depends:
- If you set up the hitch, leave everything else the same and then pump up the air bags the torsion bars will be put under greater strain. This will increase the hitch weight and increase the rear axle loading (it will also increase the front axle but by a smaller amount).
- If you pump up the airbags and then adjust the torsion bars to provide roughly the same weight distribution, there should be no significant difference (trick is to know how much strain you are putting the torsion bars under)
If you have a goal of increasing the rear axle load, simply shorten up the chains on the torsion bars a couple of links and you will achieve the same thing.
