The rear end ratio is VITAL to towing performance on the 2500 Burb.
Another poster expressed his dissatisfaction earlier in this thread with the 6.0, and the first thing I looked at was what year... yep, newer than 2007, after the 4.10 rear ratio was no longer available.
I have a 2005 2500 Burb, and have been satisfied with the towing performance at 7,000 lbs. with a 6.0 and a 4.10 ratio. I held out for that 4.10 ratio, and let all the 3.73 ratios at better deals lot rot back when I shopped for the one I have.
I think with the 7.4L, you'll still want a 4.10. I believe with the 8.1L, you'll be ok with a 3.73, unless trying to tow 10K. Anything above 10K (up to the 12K maximum) you'll probably want the 4.10 ratio even with the 8.1L.
It is quite interesting as far as fuel economy, because in hilly terrain, the 4.10 ratio actually gets better fuel economy than the taller (smaller numerically) ratios, because the 4.10 enables more of the transmission's gears to be utilized throughout the pull.
Another "tip and trick" with the 2500 Burbs... stick with the stock tire size. Do not "upgrade" to 265s. That extra little bit of diameter downgrades the final gearing, which results in a loss of towing and transmission performance.
