All of 'em!
In a nutshell: You are dealing with the same basic engine as far as torque/HP from 94-02 (second generation-2G). Also the same running gear.
Power upgrades aren't quite as easy on trucks prior to 94- but then that's not "late model".
The 03's (3rd generation) look funny, sound awful (quiet) and have a compromised interior. Yes they can be had with four doors, but a Dakota has more rear seat room. The only advantage I see to a 3G is the 48RE (auto) transmission. It appears to be the toughest auto so far.
Expanded some: The 2G trucks up to 98 have 12-valve heads and inline (the bestest) injection pumps that are mechanically controlled. 98. 5-02 are 24-valve heads and have computer controlled electric injection pumps. The stock ratings go from 160HP/400TQ 94-95 up to 245/505 in the late HO versions. Either of these setups can be easily "BOMB'ed" to make whatever horsepower level you want or can afford. 300-350 hp is fairly easy/inexpensive, 450+hp costs a bit more, and there are folks out there with well over 600hp and they've spent some real time and money on those trucks.
The bad news is that the auto transmission will need work to handle the uprated power and that costs a good deal more than an uprated clutch. Many--if not ALL the folks with the aftermarket autos will recommend that you do the transmission if you do nothing else. There is that much difference in the stock offering and the performance of a proper transmission. You'll get more power, better shifting, and super reliability from a improved transmission. Two of the most popular vendors for these is ATS and DTT, but PLEASE DON'T START AN AUTO transmission DISCUSSION HERE! They can turn ugly and PLENTY has already been posted about auto trannies on this site. I don't drive an auto, but I think I fully built one will cost around 4 grand.
The BOMB'ing begins by installing GAUGES. You MUST monitor the Exhaust Gas Temperature (EGT) and will want to monitor the Boost, transmission oil temp, and fuel supply pressure on 24v before 03.
Gauges and mounting accessories will run around $300.
On 24v trucks, first level, you BOMB by adding computer boxes which increase the fuel supplied and many advance the timing as well.
On 12v trucks, first level, you BOMB by tinkering with the various components of the mechanical pump control, and advancing the timing manually.
On both 24v and 12v, second level, you'll install bigger injectors--and depending on how much fuel you push-- you'll need to increase the size of the turbo.
The 12v's have a dowel pin that must be secured (KDP). The 24v's have a lift pump (LP) that tends to crap out with regularity.
Hope that gives you a little something to go on. Do some searches on this website and you can read for days and days. I did before I got my truck--and am still learning from the collective wisdom available here. The TDR "Buyer's Guide" outlines most of the year to year changes in the trucks. Like one I forgot-- 01. 5 is when rear
discs became standard, and pre '98 was extended cab-post '98 is quad cab, but 98 can have either one.
Also you'll want to remove the catalytic converter on 12v trucks and the muffler on both 12/24 trucks. The stock airbox should be replaced with a high flowing filter. Cheap and easy is the BHAF- Big Honkin' Air Filter.
Diesel Dynamics has a "Configurator" at their site. Dial in the truck and how much power you want and it'll give you their recommended upgrade list.
Search and Read and Enjoy your truck when you get it!
