I wouldn't go higher than 4:10s since your are only towing 10 times per year. Plus if you go with a lower gear ratio you will be able to slap 35s under that thing since you have a 6 inch lift and it will look ten times better and tow your trailer with out any problems. Hell I only have a leveling kit and I am running 35s on mine with 3:73s.

 

I don't understand the gear ratio all that much but my 06 with a level kit has 4.10 or 4.11 it came stock that way and I am running 34" tires. I haven't ran a tuner in it but seems to run fine.