5.2 magnum A833 2.93 Highway MPG

Factory 4200 pound Dakota ext cabs with a 5.2 and 3.55 gears with OD making it about 2.45 final get about 16 MPG average. Not sure exact highway vs city.

My 5.9 Dakota R/T 5.9 ext cab with 3.92 OD to about 2.74 gets about 18 highway and about 13 average.

The OP's estimate sounds about right in the ballpark to me.