Hello BC and thanks! I think overdrive was offered on the Chevy trucks, but I'm pretty sure that was not the case for the GMC V6 in the light trucks.
The overdrive I used was from a mid-eighties Chevy truck known as the New Process NP440 MY6. I used the info from this article.
http://www.customclassictrucks.com/t...n/viewall.html
Works nice with this engine and 65mph is about 1800rpms.