He's towing 6000# wet TT, he does not need a HD diesel pickup to do that! Hell I towed 9,800# with a 2500 CTD rated at 305/555 without one issue what so ever. Towing my 6800# boat over the Jellico my truck stays in 8 gear the whole way up towing @ 70 mph. Given most TT's are longer flat in the front I can't see him having any problems with that weight.
Now if he is thinking that he might get a larger TT within the next four years than he may want to look at a HD pickup. Otherwise he is just wasting his money IMO.
Don