No 5 speed in an R/T dakota from the factory.
No 5 speed behind a 5.9 from the factory.
No 4X4 dakota R/T
No long bed R/T ex cab and regular cab, no quad cab R/T
11-16 mpg in my experience
The R/T has 3.92 gears, no 3.55 bad for mpg, good for off the line
The 46 RE has a few issues that can easily be fixed

I run a 44RE in mine for more TQ off the line HP and mpg. All R/Ts had the bigger one but we have to re-build them a lot more.

A 92-95 5 speed 318 will spank a stock R/T. There is a lot of weight difference, probably 1000 lbs hard to make up for that with 42 CID and a heavy inefficient auto.

I am not causing global warming, I am just trying to hold off a impending Ice Age!