3000 stall convertor and 2800 highway cruising

Tony Fields said
Cam is the problem with fuel mileage according to folks that are in the know.
It's a Comp XE 284 Hyd.

With the 3.55 gears at 70 mph I am turning around 3100 rpm's

The fuel mileage is around 11.8 but a couple of weeks ago I got 12.2 going
to Indy and back.

That mileage isn't out of line with your combo. I have the next step smaller cam in mine but everything else is nearly identical to yours and it only gets about 1 to 1.5 MPG more than yours.