pj,
I don't know your truck but the absolute quickest, cheapest and easiest way to elevate gear ratio a wee bit is to increase the diameter of the rear wheels. For example, if you are running 19.5 inch wheels and your overall tire height is lets say 33 inches, replacing with 22.5 inch wheels might increase your overall tire height by one or two inches, thus lowering engine R's accordingly. You can go to an rpm calculator to estimate benefit. Only downside is that it makes your speedo slightly inaccurate and you end up with different size wheels front/rear.
