Slower down and it'll improve, even my 05 Magnum loses about 3mpg going from 70 mph to 60 mph and A/C makes abit of difference.

One thing to remember is the 94-01 Rams had a horrible computer tune (bunch of timing pulled out) to compensate for the inevitable plenum gasket leak that they suffered from, they call it the death flash. I can't remember who it was (SCT maybe?) but a tuner company claims around 45 HP or so for their tune in these trucks. I bet a tuner would help alot (power and mileage)