you have to be making big numbers to need to do any real upgrades to this trans as far as im concerned, my chevy is kicking out around 550 hp and about the same torque on just a stock gm nv4500. the only thing you should do is weld the 5th gear nut on, i did it on the chevy but havnt done it yet on the dodge. dodge nv4500s dont have a balancer at the end of the 5th gear nut like chevy units come with so the 5th gear nut comes loose very easily, my chevy one was loose when i purchased the trans from a truck with 200,000 miles and it has a balancer. Youl have to buy the tool that fits the nut or i made one out of some scrap metal and a few bearing races and a pinion nut. what i did is just tighten it up and then weld it in 4 spots, a tack weld at every groove of the nut, that way the balance is even.

another thing you should consider is a short throw setup, i dont really care for one on my dodge because its not a very sporty truck but i wanted one for the chevy, nobody sells one for my chevy so i made one myself. you can buy one for your dodge but you can save money making it yourself if you want to. what i did was just build a 1" spacer plate for the shift tower and then knock the roll pin out at the botom side of the shifter, remove the isolator o-rings, slide it back in place but leave it exactly 1" lower then it was before and weld it in place.

heres a few pictures of what im talking about
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and this is what a stock one would look like
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