hey john,
i would use the combined weight of 7700# for both axles as accurate this individual could have a lot of error i assume.
for the reciever issue i replaced my 2004 factory one with a 2014 one, so the ratings are much higher and it has a 2" sleeve to dummy down the 2 1/2" so 2 1/2" or ratings is not an issue for me (below is a picture) ps bought the hitch for $5 ;)
i actually replaced a lot of things on my truck, i replaced the tranny with one out of a 2010 5r110w, rear diff with one out of a 2010 with aluminum cover and bigger brakes, swapped my stock leaf springs for a 2007 front diff with coils and bigger brakes as well. my 6.0 has been fully bulletproofed with upgrades that would make your head shake (+$30,000) althought the truck aint clean and has a mismatched canopy that makes it look like a toilet as well as missing a grille, its one of the best tow rigs out there drivetrain wise. As well as changing the interior over to a 2014 king ranch besides the dash, new tow mirrors with all the power functions, 2014 tailgate with camera (wanting to add camera inside the trailer and on the back, going to screens on the dvd deck, rear view mirror, and edge programmer, all which could be a different screen or changed intermittently.
below are pics of my A frame i could take better ones tomorrow once it gets brighter. i think in your question i have channel iron. ill let your respond on the next steps for our converstation, again i appreciate your help 110% the local rv dealership guys are useless.
steve