If you want granny low and overdrive, take a look at the NV4500 that was used in the late 3/4 an 1 ton GM and Dodge trucks. There's also the 6 speed (Getrag i beleive) that has been used in GM heavy duty pickups the past few years. Contact Advanced Adapters, they make the kits for doing the conversion.
You could also consider using a Gear Venders overdrive, which can be used beind virtually any trans. It's very similar in operation to the old Borg-Warner od that many of us have in our 1/2 tons. I've even seen them put behing NV4500s to get a double overdrive.
One other option,Advaned Adapters also manufactures the Ranger overdrive, which is an auxillary trans that mounts ahead of the main trans. It will move the tranny back about 7". They make them in over, under, and combination over/underdrive.
