My Wifes Aunt bought a 2001 2500 x-cab long bed 4x4 auto Cummins new. Used about 40% to tow a horse trailer, empty 60%. At 50K miles the front end was first worked on. Her cousin is a mechanic and she only had to buy parts which were close to $1,000. The truck currently has 75K miles and the tranny has been worked on twice, front end once. I got a chance to run stock to stock against the F250 at up to 75mph it was pretty even. Keep in mind at the time the 2500 had 55K miles the F250 had 190K miles. Got a chance to run it against the Excursion and same thing. At the time the 2500 had 70K miles, the X 160K miles. Her husband (wifes Uncle) had a 97 F250 he bought new same truck as his wifes 4 years later only Ford. When he traded the truck in at 330K miles for a 04 F350 the front end was worked on once and it had a torque convertor, one belt at 225 miles, and one cps.
By way of comparison the F250's front end was first worked on at 150K miles and the X at 165K miles. Ball joints are common to fail on the driver bottom side and the hubs can fail and cost $200-500. The Excursion had one replaced at 165K miles and the F350 at 124K miles. The F250 has it's originals at 240K miles. Between the three diesels one tranny has been replaced, 500K+ miles, not possible with a Cummins/auto in 99-02 trucks.
The 7.3's can leak fuel which is usually the two o-rings on the fuel seperator valve ($40 at Ford). There are also two common oil leaks, one caused by o-ring failure in the HPOP, the other due to the turbo pedistal leaking. CPS's can fail at any time on the 7.3's. I paid $100 for one but they are selling for $20 on some Ford forums recently.
Things I've done to the three psd's.
Alternator, water pump, fuel seperator o-rings in all three, turbo at 55k miles in F250 warrantied/tranny at 83K miles, driver window motor, driver mirror motor, door lock actuators(6), ball joints, hubs, rotors, callipers, leaf springs, power steering lines/pump, fuel heater elements, pcm, pulley tensioner at 225K miles took out belt.
All in all the trucks are pretty tough and figuring the abuse the F250 was given in the past 6 years and over 200K miles it still runs and drives very nice.