Performance mixed with fuel economy!?

A 318 gets way better milage than a 360, but the key is the transmission. An OD 42RH or a 46RH will help get you the highway mpg..2wd mid 80s dodge vans.....a 3.9 would have the 42rh a 360 the 46RH 318 either have to check. A gear vendors od might be a less expensive solution ultimately.