Don't know if a chip would be the ideal first upgrade for towing 24k. I would look at things like bigger tranny cooler, 4 inch exhaust, big intake, some gauges, after those upgrades check out totaldieselperformance.com for a wildman 4 pos chip. If you plan on towing 24k regularly your trans proly won't last too long without a build up. Some other upgrades good for towing are a spearco 6L intercooler, and the turbonetics replacement turbo. You probably already have a way to stop all that wieght too right? Big brakes.
That would be the things that I would look at if I were in your position. Good luck