Fully Chipped that Cummins should pull the trailer and a couple of Oak trees. My STOCK 6.6 Duramax does just fine without the added expense and doesn't void the warranty by adding the chip. 397HP and 745 LBFT lets it do its thing fairly well thank you. My 5'er isn't 16K but gross it's just under 14K. SRW is fine for this but I agree a 1 ton dually is needed for anything larger. DEFINATELY go DIESEL. I don't think anyone makes a gas engine large enough for effective towing on a rig that large. The 8.1 492cu in GM is GONE. BTW -- Mallard -- NICE RIG!!