Trucks slows and drags when coasting

That's normal operation and can really get one's attention when it occurs. I also have a 2014 Ram 1500. Mine was a crash rebuilder with 4,200 miles when I got it. What you will notice is the transmission downshifts to slow the truck, then as it does slow down, you'll feel it let go and coast easier for a few seconds, then it will do the same thing in the next lower gear, until you get down to about 25 to 30 MPH.

This operation greatly reduces how much you have to use the brakes, especially in city driving. It's also cool when you suddenly hit the gas and launch off into the stratosphere. The transmission is already locked up and ready to go.

As a point of interest, my friend owns a body shop where he specializes in rebuilding smashed one and two-year-old Dodge trucks. He did mine four years ago. The State Patrol comes right to his shop to do the safety inspections, and through word-of-mouth, he has built over a dozen Dodge trucks for them. A have another friend who is a retired county deputy. He also has a Ram and tells me they call them, "the sports car they never had as a kid".

Do you have the 6-speed or 8-speed transmission?

I got mine up to 22 mpg average on a long trip, but now with snow on the ground and extended idling to warm it up before I take off, it has dropped as low as 13.4 mpg. It does come back up again a soon as I start driving, but it seems the instantaneous reading is more relevant.

I also learned it will not go into "Eco" mode if the Check Engine light is on or when I use the steering wheel switches to manually limit the highest gear it can go into.

The only other thing I can think of is this is the latest version of computer-controlled learning transmission that Chrysler developed for '89 models. If the battery is disconnected, clutch pack volumes have to be relearned as well as sensor data. It's normal to experience unusual shifting characteristics right after that, but that rarely takes more than a few miles or a dozen shift cycles to complete the relearn process. Most of the time you don't even notice that.