I have one and enjoy it, I get 16-17mpg highway and 13-14 around town. I have 73k on the clock, and it runs quite strong. Things to date:
Thermostat housing leaking (replaced under warranty ~24k mi)
TPS sensor (~60k miles) 23$ from Advanced Auto
Rear speed sensor (~66k miles) 30$ from Advanced Auto
Normal oil / rear / transmission changes along the way.
I suggest never letting anyone flush the transmission in the D. I have heard both sides of the fence on this, and I wouldn't do it. Drop the pan, put a new filter in, and adjust the bands.
There is a TSB for balljoint replacement from years 00-03, covered at the dealership. (read free) I would highly suggest getting the D checked for ball joint problems, and have them replaced free at the dealer. (Thanks mopar for non greasable joints)
Transmission is the weakest point in the whole drivetrain, I would expect the tranny to die around 100-170k if the last owner took care of it. Some people have nearly 300k and still have the stock transmission but I wouldn't count on getting that far.
Check the owners manual and see if it is labeled as a 'premium fuel only' D. In 00' when the R/T came out mopar added a more aggressively timed pcm to the vehicle (not as aggressive as a mopar performance pcm) which required that you ran premium fuel. In 01 I believe midway through the run they switched back to a less agressively timed pcm which did not require premium fuel. On this note, you may want to read any work orders that the previous owner may have. There is a 'death flash' to the pcm where if a customer comes in complaining of pinging, they remove so much timing from the pcm the vehicle feels very doggy.
Things that are different from an 01 SLT with similar options: wheel / tire combo (17" r/t wheels), R/T embossed seats, upgraded shocks (which I would still replace with monroe sensatracs), louder muffler with polished tip, and different pcm.
I have a FM cat back + mopar pcm + fastman TB + IP 3 cia on mine, and it does what I ask it to do. I have towed my car through the mountains from MD > PA and you know its back there but it tows it just fine. I added firestone airbags to level it out when towing. I tow probably once every 3-4 months with it. Works great as a people mover and the seats fold nearly flat for larger object moving also.
If you are looking to tow things more frequent I would suggest stepping up to a larger truck (ford 250 /dodge 2500) with the diesels. I've towed my car behind a ford excursion with the 7.3 and you don't know the car is behind you. The added firmness and weight of a larger vehicle when towing frequently is priceless. I don't tow frequently so the D does what I need it to do.