Does anyone know how to increase horsepower with a straight six engine and 3 speed tranny?

 

Personally, I love that truck/engine combo. I've had 2 trucks, and 3 vans with it. As far as power goes, it depends on what you are trying to do. Correct me if I'm wrong, but that year is carburated, isn't it? Old school power options like open element air filter and a better exhaust should help. If it's off the line help it probably could use a better set of gears. I think they came with 3.08's???? Maybe look into slightly steeper gears. It's too bad it's not a stick, b/c I always felt that my trucks had good power, but the vans were autos, and heavy, so I feel your pain there!
Hope this helps!!!

 

exhaust, intake, cam, header,,,