The amount of lift has EVERYTHING to do with the weight distribution. More lift generally equates to more pressure on the bars. More pressure is more weight distribution and more sway control.
There is such a thing as too much lift, and you end up bending the bars or something on the truck or trailer.
Did you find that putting the bars on was any easier or more difficult than it was last year?
The truck sagging more indicates more weight or less weight distribution. If you didn't inadvertently add a bunch of weight, and you can verify that, then your WD hitch is out of adjustment.
You probably justforgot how it went together over the winter, and are off by a hole or link or whatever somewhere.