Towing a 5th wheel trailer,

Hello
I have an 06 GMC Sierra crew cab Z71 package,
1/2 ton i,m looking to either get a 3/4 ton pickup or upgrade my truck with extra helper springs, 8 or 10 ply tires, with a diablosport tuner, and a k&n air filter system, ive been getting diferent stories on what i should do, I curently get 16 to 17 miles a gallon, should i put the extra parts on my truck, or buy a 3/4 ton truck with better axles an springs, but lose on gas milaege,or upgrade my truck an hope i can keep good gas milage, because it is a daily driver, anyone have athe correct answer or the correct way to go about this, we are towing a 28ft 5th wheel,
ive heard put air bags on it, put bigger springs, an put 3/4 ton rear end because of the extra bearings it has on the axels,
anyone know of a correct way I can achive this without breaking the bank, and is there alot of diference between my truck and a Dodge ram 1500 package,
Thanks
Tom Benoit