you will want a 99-03 for the new body style with the 7.3. preferably a 99.5-01 with the forged rods if you plan to throw bigger injectors in it.
i just sold mine and loved it and if i was you i would find a six speed.
got a duramax now......
my truck was a 97 modded out.
i wouldnt limit yourself to under 100k either just my .02
these trucks run into the 4,5,6 hudred thousands with little issue.
another thing to consider is the Crew cab long bed. i owned mine for 3 years and loved it. but it wasnt very fun to drive around town and park and turn around or to flip a U turn. if you got a big family that is cool if not the smaller the better.
a great forum is fordtruckenthusiasts.com go to the 99-03 section and learn some if you havent already.