So I got a chance to do a little tinkering with the truck tonight. Got the tail lights taken care of.
Man there is some scary wiring under the bed. Mainly for the brake controlers (one for regular hitch and one for gooseneck). The wiring includes household wiring and wiring nuts.
While I was under there I noticed the scrader valve for the air tank, filled up the air tank and the air bags work! No on board compressor, but no biggie.
Measured the exhaust, its 4"