Looking to buy 2015 1500

Getting ready to replace my 240K mile 2005 Chevy with a V-6, 8spd crew cab RAM. Have a few questions before I pull the trigger.

I read that the 2015 has a transmission warm up feature that uses engine coolant to warm the trans fluid (this will reduce viscosity quicker and helps fuel economy). I wanted to know if there is a way to bypass this (guessing with a programmer)? I've always installed a large external transmission cooler on my cars/trucks that will keep my fluid temps around 150 degrees. This helps the trans live a long life because heat kills automatics (I've never had a transmission problem and I put a ton of miles on my vehicles). I'd be fine with the trans warming up quickly, but once it does, I want the fluid to go through an external cooler, then back to the trans.

Is the 8 speed trans behind the V-6 the same as what the V-8 trucks use? How about the Ecodiesel? Just curious since if it will hold up behind the higher powered trucks, it should live a long time with a V-6.

Wondering if it is a good idea, for gas mileage, to run the 20" wheels/factory tires with the 3.21 rear gears. All of the 20" wheel trucks I've seen have the 3.55 gears. The 3.55s and 20" will turn the engine about 100 RPM higher on the highway over the 20" with 3.21s. The advantage of the 3.55s may be that the truck does not downshift as much trying to maintain speed.

Thanks for any advice!

Welcome aboard!!
The 8 speed trans should be the same across the line, I think it would cost more to make different versions, they just make the one.
The 3.55 gears will have more pull down low and tow more over the 3.21. Of coarse the 3.21 with the V6 is the ultimate fuel mileage saver before you make the jump to the eco diesel engine. If you don't tow, you may be happy with the 3.21, it is offered by Dodge on models that you can get 20" wheels on from factory, so there are people with that combo. So Dodge has designed the truck to work nicely still in that configuration. A friend of mine bought a V6 Ram with the 3.21 but has 17" wheels. It has plenty of pep off the line and when you hit on it, he drives very conservatively, so if he put 20's on it I doubt he would notice much difference from his driving style, he would still be happy and have enough grunt for how he drives.

The 8 speed is differnt between the hemi and the Eco diesel. The hemi and Eco diesel have the same 8hp70 and the pentastar uses the 8hp45 and the hellcats(useless info) uses the 8hp90. The gear ratios are the same across the board. Your not going to like this but the 8 speed runs warm by design the engineers like the 8 speed to run about 180 and its a "life fill" I'm sure I would get mine changed if I had one. My 6 speed doesn't get above about 130 unless I'm towing these trucks hav factory Trans cooler. The 8 speed is a ZF transmission and they are tuff the only issues I have seen with them is the some issues with programing witch a flash will took care of.

Get the 20's you will be happy you did the 3.55 or 3.21 really won't yield you enough difference in fuel economy not to get them both rated at 25 hwy. My choice would be 3.55 incase you ever want to tow anything. The 3.21 axle is rated for 4500 lbs ish and the 3.55 is 7500-8000lbs that's the hidden difference.

To add to what was said above, the transmissions are designed to run warmer, ie the fluid is designed to take the higher temps and not breakdown like the older fluids you are used to. Also the v6 uses the 845rfe, there is a 8hp45 but chrysler had zf add some things to it to increase the torque capacity and it became the 845rfe.
How much if ever you plan on towing will determine your gear ratio. I have towed with the v6 8 speed combo in my wife's grand cherokee which has 3.45 gears and no matter what I wouldn't be towing over 5k with it but that is just me. The rental I had a while ago was a Hemi quad cab with 3.21's and the 8 speed and it c9ukd easily get 20 Highway in 10 degree weather, so that would be the route I would go if I stepped back down to a 1500.

thanks for the info guys, it is all very helpful. I rarely ever do any towing but when I do most the time its just landscape trailer loaded with mulch or dirt. I will occasionally trailer a car, but that is extremely rare. I know the newer fluids are designed not to break down in the heat, but I just don't like the idea. I guess what I would do then, is just change the fluid more often.

A quick mention regarding the 8 speeds. To my understanding, ZF manufactures the transmissions that are supplied on the V8, while Chrysler manufactures the 8 speed transmissions under license from ZF for the Pentastar V6. Eventually Chrysler will manufacture all of them.

If I were going with the V6 I would opt for the 3:55 ratio. That's a nice all around ratio that wasn't available to me with the Sport 1500. If it was I would have chosen it. Also great for towing. 100 rpm is negligible regarding economy and I'd bet you're right that it would "hunt" less with the 3:55 setup. Is limited slip available? If so, get it--you'll be glad you did.