Hi SCummings.
Depends on what you want to do to your truck.
If you aren't going to do anything to your truck a '98. 5 - 2002 24V truck needs a Pyrometer (EGT gauge) and a Fuel Pressure Gauge at the bare minimum. WHY DIDN'T THESE COME FROM THE FACTORY

!!
If you plan on doing som HP mods then your Pyrometer probe should go pre-turbo, otherwise it should go post-turbo so you can moniter shut down temps.
If you want some daily liveable HP I'd say go with some DD1's or DD2's and an Edge COMP.
About package performance options, In My opinion it is better to piece your own package together. I'd say go with a popular air filter here at TDR, the BHAF, See my truck bio in sig. For Exhaust setups, go for whatever you like,, make your own if you have the time, by a 4" system or piece one together yourself. The Dodge Cummins 2500 and 3500 are one of the last "Hot Rod" trucks out there,, these trucks are "New School" you can mod these trucks up, Just like you could mod a 1968 Camaro, except now it is Higher Technology, (Chip's, Turbo's, different injectors, etc. )
Hope these help,
MerrickNJr