My take -- solid engine, somewhat underpowered by current standards, questionable transmission that WILL need repairs or replacement if you're towing a lot with it.
Sounds like your mech is a big 7.3 fan, and there is no issue with that. But this is still an 11 yr old truck w/ 11 yr old tech. I do not mean to commit heresy against the sacrosanct 7.3, but I don't think that the 7.3 is statistically more reliable than, say, an '06-07 LBZ Duramax or an '04-07 5.9 Cummins. But those have more power, and far better (and in the case of the LBZ, far, far better) transmissions, while still being "pre-emission."
Just some anecdotal evidence for what it is worth. 2 contractors on my street run several trucks for their businesses, and were both die-hard 7.3 fans for years. One got tired of replacing transmissions, bought himself an '09 Dodge Cummins a couple years back, and has since pretty much replaced his fleet with Dodge Cummins trucks. The other got tired of buying old 7.3's to keep his fleet current, finding problems, replacing transmissions, etc., so he finally broke down and bought a '12 RAM Cummins at the end of last year. They both kinda laugh at themselves now for dumping $$ into old 7.3's for years. FWIW.
Good luck!
