another thing to consider on these dodges w/cummins:
its not that the engine can't be reliable turned up for more power the exact same engines are in heavy equipment and medium duty trucks making 100 more HP than the ram pickup. the same 160HP version that is in both my '92s is the same as the 275HP version in my buddies '95ish freightliner box truck.
Anywho, its not that the engine cant handle being turned up w/in reason; its the rest of the drivetrain that isnt necessarily designed to handle the doiubled HP you can produce. dodge automatic trannies are generally considered the worst autos out there. i have had to have them rebuilt in stock CTD trucks that were not abused. also, dodges have their issues, that your gonna see in any dodge truck, but they may present themselves earlier in a truck thats been abused.
I think, in general, (and i am NOT trying to stereotype) I would not buy a truck from a younger kid. its just my gut feeling its been abused, and it seems hot rod diesels are about as popular as rice rockets these days. every kid in town here has a late model diesel they race around in. i would look for a truck with stock tires/rims, not alot of extra gauges, stock exhaust, etc. also, be sure it has the stock air filter, and air filter piping. even one that has a GN is not necessarliy bad; the trucks are built to tow.
Overall, a cummins engine is in a league of its own, when compared to its V8 powerstroke and dmax counterparts. it is a medium duty engine in a light application; not a light duty engine in a light duty application. it is built like most all other diesels; 6 inline cylinders, lots of iron, lots of weight-which means heavy duty.
There are still good, unmolested trucks out there, just have to keep your eyes open.