I have turned up the following supplier of an overdrive module=> http://www.gearvendors.com/
.. that bolts to the rear of an auto and effectively gives you an overdrive ratio, but also gives you split shifts between the gears.
So a C4 ends up with 6 ratios: 1, 1 1/2, 2, 2 1/2, 3 and an overdrive. Sounds like the best of both worlds and you could get an older muscle car performing like the new factory performance vehicles - great acceleration AND economy!
Apparantly these units can take the grunt of a modded 8.
Has anyone out there had experience with this manufacturer before I order one?