Depending on the setup in the rear of your truck, you may be able to remove the spacer blicks underneath the axles (put them on top so you don't have to replace U-bolts.  That could hypothetically net you 1-2 inched lower in the back.  Check out the TDR (http://tdr1.com) for posts from folks who have been there, done that on the Dodge.  Other, more costly alternatives include a lowering kit for the truck or lifting the trailer.

LAXPatrick

http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=3134

This thread talked about clearances...