Changing to anything less than 4.30's from 3.73's isn't worth the effort and cost. One could argue that even 4.30's aren't worth the cost for the gains you might get.
That said, you'll need to define what the edge of the weight capacity is, and what kind of RV you're pulling, fifth wheel or travel trailer. Because even with the gas motor you have, to reach the 'max weight' a 2500 is rated to pull, with a fifth wheel you'd have a pin weight that would easily max out your payload before you put anything in the trailer or truck. With a travel trailer you'll have considerably more room to pull a bigger trailer.
Remember that gearing doesn't do much other than allow you to move the load better, it won't help you keep it stable. If you're planning on going to the max you can haul with a 2500, you likely should have stepped up to a 3500 to give yourself some cushion. Running at the max capabilities of a vehicle isn't something I'd advise doing long-term. One or two trips a year at less than 50-100 miles, sure, but constant or on a longer drive? I'd want more truck.