Is that a 5000 rpm stall converter you've got? If so, this could be the reason for needing to get the rpm up so the car will move better, and that high of a stall won't help with gas mileage.
Yeah it's a 5000 stall but when I first start it up and shift into gear it Def don't act right I have had many mopars and none have done this...but after moving it around a bit it's acts fine