New to the Forum: I have a 1987 Dodge D-100 Ram. I bought it new and have stored it 25 years. I have had the interior redone and the engine rebuilt (1000 km on new motor). The cam is a little bit lopey but does not adversely affect the driveability. It is a 4 speed on the floor(1st,2nd, 3rd with overdrive). I would like to convert to a 'super six'. I have a two barrel intake manifold and breather. I would equip the truck with performance a exhaust. I don't think that I would need a kick down rod as I have a standard transmission. With a change of rear end would the truck have any appreciable increase in performance?

Yes.

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Too many people who were born on third base actually believe they've hit a triple.

Be careful with the rear end gear ratio. It will depend on how you use the truck, and the tire size. If you gear down (higher number) you will help with pulling power at lower speeds, but will limit top speed om the highway. If you gear for the highway (lower number) you will limit your pulling power. Plus, those trucks have a comparatively small clutch, and if heavily loaded you will be really stressing the clutch. Ask me how I know.
I have a 84 D-100 slant six 2bbl, A-833OD trans and 3.91 rear ratio, R225 x 70x 15 tires. If hauling my race car, I have about 500-800 lbs in the bed, and just under 5,000 lbs in tow. I need to slip the clutch pretty good to get going from a light if on a uphill grade. I'm actually considering adding a turbo at low boost to help (if I get some other projects done first).

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225