If you tow regularly, you'd be best with a 4.10 gear ratio. With the OD off it should run around 2750rpm @60mph. I tow with my 360 on weekends and 3rd gear (1:1) runs be about 2600rpm at 60mph with 3.92 axle. Adding a cold air intake may help your midrange out. A good one will run about $150. I noticed a nice gain with mine when towing! Of course, your results may vary. The gear conversion shouldn't run more then $500. If you wanted to get really aggressive, you can upgrade to 4.56 gears. I think that's the maximum size that will fit in the pumpkin.
These guys are quite reputable:
http://www.yukongear.com/
