If it helps, in a B-body, with a Hemi (now 502 ci and 600+ horse), 727 and 4.10 Dana, 2800 converter (Dynamic TCT), went from 10 to 14 mpg on the highway.

I wouldn't/couldn't run the 4.10s without the GV. Around town is still about 5 mpg

I hear it's an easy fit for E-bodies.

The 12 Scariest Words in the English Language: We are here from the Government and we want to help you. 1968 Plymouth Road Runner, Hemi and much more 1968 Dodge Charger, 318 and not much else 1958 Dodge Pick Up, 383 and loud 1966 Dodge Van, Slant 6 and cool