I had added the overdrive 5th in my last Pantera while I had the ZF out for some other work. My engine was just over 600 hp and had 180 degree exhaust. The RPM at between 75 to 80mph went down from 2800-2900rpm to 2200-2300rpm. I did not notice any droning although my exhaust was loud anyway, but with the windows up I did not notice any noise from gear box. Gear was about $1500 from RBT.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.