Jim, I have an Ahmed chip and I believe that fuels on overrun as standard to cool the piston crowns.
The 'chip' in the RST has nothing to do with fueling.. it is only ignition curve.
Im not a master mapper but i dont see how it can be 'set to overfuel' on overrun...
The only way to adjust the Ke-fueling is via the meetering head and i only know a coupple of people who are able to do this.
Im afraid I have not been that impressed with any of the tuners Ive visited so far and Ive got no faith that it I go to another one they will be any better.
There is no point going to any old tuner You need to choose the right one... someone who knows about modified fords ZVH/CVH/Zetech difference etc.
My recomendation would be Karl Norros although he is prob Very busy at the moment.. otherwise why not try Stu @ MSD ive not heard a bad word about his work yet
CheeRS
Phil