Eaton 12 spd auto

Company trucks in our fleet are automatic and they pull a lot of mechanical RGNs. I only have heard issues when they get stuck or have to raise their air suspension. The latter doesn't even pertain to your question and is an easy fix from the factory.

 

They do good.Ran one 1.2mill no issues and always hauled 45k and up.

 

I am running the 18 speed auto shift on 3 trucks 2 dump trucks and 1 Lowbed with Murray mechanical rgn I like it but it is not as smooth as a clutch the standard program from the factory will need to be changed I like the performance shifting program I find the heavy haul configuration is too aggressive you will want the blend pedal clutch configuration in reverse and low in your primary shifting program blend pedal makes your throttle pedal work as the clutch for the first part of the travel until fully engaged then it works as a throttle again you can also drag the brake in this mode there is just a ton of things that can be programmed into this Tranmission and the dealer was not much help you will need the eaton rep to go over the options with you to get it right
Now for the 12 speed I don't think the ratios are correct for the application and I have heard that the paccar 12 speed has aluminum case and they have had lots of failures on low mile trucks I don't know if the paccar and eaton 12 speed have anything in common but due a lot of research before buying a 12 speed.
If you are going to spend the extra $ for the auto shift I would go for the 18speed the low reverse is what you need to for the RGN

 

You'll be fine with the 12 speed. Those transmission have the back up assist or whatever they call it so that you won't bump the trailer while hooking up.