i recently lifted my 2005 cevy 2500hd diesel 6'' and installed 35'' tires on 20'' rims.will these tires put to much strain on my allison trans without installing gears.if so any recomended ratios??i drive this truck every day in town and highway.and would like to know of any mods to get the gas mileage back up..  

Gears may help gas milage alittle, but are not really necissary on a diesel. THe nice thing about diesles is that you can increase fuel milage but upgrading them, with a chip, new turbo(or duals) air intake exhaust...  

regearing would help releive strain on your tranny and help it live a little longer. you would also reagain lost torque and horsepower for better towing.