We’ve had some get 300,000 and still work like they always have.The bodies are more the issue in the snow belt.

Ive seen 400+. The trans needs rebuilt during that time maybe 2 or 3 times if I remember right. The obs trucks are better.

A well taken care of 1999 7.3 Powerstroke engine with normal use and good maintenance is good for about how many miles?

500k+ as long as you fix things as they come up. I do not think you will need a transmission rebuild at all, the auto and manual transmissions are excellent in those. The most common things for that year are definitely injectors, o-rings on some of the HPOP stuff, and if you have a manual transmission, you likely will need to upgrade the fork at some point. No matter the case, check out FTE, you can see the posts by the engineer who designed the auto transmissions in that time frame as well as the next gen, and lots of good info. White Bear Lake Ford for all your parts, they are 10% over cost, cheapest in the country I can almost assure you. Rock Auto at various times will have just a few things that beat the price, but I have been ordering from there for 10+ years now.

I also would recommend a 6.0 over the 7.3 though for a lot of different reasons, but the main one is much more power, and all of the issues i'm sure people are about to chime in on have been fixed. My 2004 F350 CCLB 6.0 6 speed manual has 244k engine and transmission all OG, just replaced the rear 2 brake calipers and front brakes. Ford made them again, so to get a new caliper with pads for 75 bucks is a steal to me!