I've got a 1992 Mack CH613 daycab pulling a 2009 Jet 42' aluminum trailer.  When I'm down to less than a quarter tank of fuel, I'm usually around 24,700#.  I can't quite haul 1000 bushels of corn legally except in the fall when Iowa has the 10% exemption in effect (then I can haul more, but usually don't go over about 84000#).

I agree with the other posts that you can't possibly be legal at 80,000# under the federal bridge law formula.  If your state uses that be prepared for a hefty fine from the DOT if you're caught.  I also have a 30' aluminum dump trailer that I used to haul corn with and I got stopped with 75 or 76000 on and can only legally bridge 73,500 with that outfit.  The fine(s) cost most of the next load.

Mike