I'm towing a Jayco 32 BHDS (36'5" long) with my '99 1500 ECSB 4x4. I swapped the rear springs for a set off a 2500HD. It helped, but by no means did it (or did I expect it to make) the truck a 3/4 ton. It helped some with the sway, that being said, as soon as money allows, I will be upgrading to a 3500 SRW. As far as the swap, it was a fairly easy swap. Just had to cut the front left bolt off because of the way GM put it in had they put it in the other way, it would have come out w/o cutting. Then I had to have longer u-bolts made by a local spring company. I wouldn't think a OBS would be any different.