shopping for CTD Ram 3500

Big difference in those years... end of the 24V ISB era, vs. the start of HPCR era. The body style changed in '03, as well. The newer style had a larger available rear passenger area (with the quad cab), but worse aerodynamics.

Not really... the '03s had a couple of minor issues when first introduced (PS hose that would 'buzz' - fixed by changing the hose with a new revision, alternator bracket prone to cracking - again, simple fix, couple of recalls to waterproof the PCM connectors, and replace a tranny cooler line that was prone to cracking). Those were all TSBs or recalls, and were probably addressed by the original owners.

Regarding the 24v ISB versus HPCR: Is the HPCR an improvement, and worth paying extra (factoring out the book value on the model year)?

Bill

IMO, yes. Stock power is higher, and the engine runs smoother and quieter.