All I've done to my 03 mounty is E-fan, K&N cold air intake, and chop the third cat and put in a Magnaflow exhaust. I pull 9.974 in the 1/8 mile and I'm faster than my buddies turbocharged jeep Cherokee that was dyno'd at 280hp (its stock was probably around 190). So evidently my mods have helped a bit.
I was looking for a nice set of underdrive pullies but didnt think the cost was worth it, but I'll go with steeda. 4.10 gears are my next mod followed by a nice tune. =)