Guys, dont listen to all these 3:73 haters
I've had my share of diesels, and the issues that come with the emissions, so the 6.4 was a easy choice for me. I struggled with the 3:73, 4:10 choice. I drove both several times on the same roads to "feel the difference" between the two. On the few flat stretches of the road, the MDS kicked on and off about the same time between the two. I think the 3:73 MDS is programed differently than the 4:10 gears, making the "4:10s will allow the MDS to kick in more offten", a mute point. I chose a 3500 SRW CC Tradesmen. No plan on changing tire size or exhaust. Just keeping it stock.
I tow everything from my mowing trailer to my 11k 38'tt, to a 12k mini. I live in upstate NY, not in the mountains, but no where near flat either. I average 13 around town, and 18 highway, hand calculated. Towing 12k 7-8 mpg's. 17k miles on the clock with no regrets.
This things a towing beast. Tows 12k up these hills easily. I realize im close to my max towing, but at my age, my next TT will be smaller, and the amount of heavy towing will decrease over the next few yrs.
Friend of mine pick up the same truck as mine, but with 4:10's. His milage is worse that mine, but he only has 3k on it. Also think he may has a case of "hemi foot" lol.
Bottom line, 3:73's are very capable. Dont be afraid of them. Yes I agree if you plan on towing heavy often get the 4:10's. But if 90% is DD, the 3:73 may be the best choice...