I had 265/75/16's on my f 250 with 3.55 rears. after going to 315/75/16's i have a hard time pulling loads. Since the IDI has small Torq and HP im trying to figure out the best tire size to go to now. I figured out that a 4.10 ratio is equivilent to 4.5 in drop in tire diameter which puts me much smaller that the 265/75/16's. What size should I run on this truck?