new tranny for my 70 c-10 shortbed

[65ChevyNova]

I have a 70 c-10 with a 292 inline six with a granny 4 spd.

I'd like to get a different transmission, possible a 5 or 6 spd to make the truck better for a daily driver. by the time I hit 30mph, I'm already in top gear.

any suggestions?