Tire size for towing

[DEEZRACING]

I have a 99 chevy extended cab 4x4 with the low horse power low torque 5.3L. I have regeared it and it actually runs great until I overload it with a trailer that weighs almost 9,000 pounds. I have a 7 inch lift and currently run 35 inch tires on it. I am contemplating putting some 33's on it cuz I need some help when pulling up steep hills. I am curious if doing this will even be noticeable. Thanks