ok, to start off, cummins is a far better motor then a powerstroke.
im a ford guy at heart but facts are facts/ sure they arent fast (specially a 12v) but with the right know how and a lil effort, they can make great power and decent economy.
however uf you think your gonna get 20 mpg with 37's, your wrong. maybe 13-15.
as far as lift kits go, bds sells a 4.5 base kit for 1600.
however you can get a levelling kit (300 bucks if you do it yourself) and run 33's (see my show off your truck thread), my setup is leveling kit and 33" nitto mud grapplers, and it does great offroad. Keep in mind if you wanna flex like a jeep buildin a dodge is the soo wrong way to go.
now. as far as twins, your gonna be up in the $20,000 budget to build a 96 to handle that. and did this "fresh tranny" come with a reciept? if not you cant garauntee u should have the tranny checked over before anything.
and the problems with the 47rh+47re transmissions is mainly oiling, and weak converters.
depending on your tech know how you can build a serious duty auto for around 4 grand or 5.
mine had a rebuilt one installed before i got it, with a heavy duty converter (good for about 450 horse) for 2400 bucks. billet shafts and throttle body work are the main weak spots once ur into the 600+ horse range, which ill probably never reachw ith this truck
diesel power magazine ran articles called building on a budget,
ill link you to their site, as well as to bds's site for the 4.5" lift.
if you have tools and general knowledge of vehicles, this is a driveway weekend job, with a good name like bds.
say rough country, you might have to improvise a bit. ( sometimes tricky)
my dodge is a 24valve, and it is wayyy faster then 12 valves, but it is limited on its amount to make power. 12 valves can be built to make as much as 1500 horsepower and more.
one guy in a diesel power magazine made 1300 horse, while running 100 psi of boost (wow)
id be scared to run more than 35!!!
if you go over to cumminsforum they have tons of useful info and friendly members.
links!!!
BDS
diesel power recipies budget minded
i also read that according to diesel power, the 96-98.5 (early model 98's are 12 valve, but have the new interior, reffered to by diesel power as the holy grail truck haha)
have a stronger transmission and better injection pump (and i have a new injection pump in mine, reciept for 2000 plus install last year)
which are pluses for you.
first thing id do it turn up the pump and change every fluid.
then have it dynoed so you have a baseline.
then add mods and dyno so we can see what kinda gain u have (plus then u have a dyno sheet, which is respectable)
and good luck, welcome to the cummins owning club, hope you didn't give up the ranger but i guess if you did it happens