I have 190 30's and a stg 2, it works pretty good for towing, a 2.5 might be ok if you have stock size tires and or lower gears then 3.73, but the safe bet for towing would be a stg 2. I run 35's with my stg 2 and I want to go with 4.30's.... It seems like I need to drive 75mph to keep the truck in the power band With my setup. The the bigger turbine on the 2.5 would only exaggerate the problem.