Been a while since I had a bumper pull but did go through some of this with my 1500 Chevy. When you are all loaded with the bars pulled tight where are they in relation to the trailer frame? If you've really sucking them up tight, with very few chain links between bar and hanger then you need stiffer bars, if not then you should be good. I wouldn't worry too much about how you need to jack up the trailer to get it linked up, though that might be a good indicator of needing heavier bars.
However with only a smaller TH and a 2500 you shouldn't need much. What year is the truck? On my 2005 2500 HD I had to add air bags for my 5er to be level, same trailer on my 2013 truck and it brings it down to just level, definitely higher payload on the newer ones.