Can't go wrong with a 7.3 PSD... I got 4 of them (running, not counting the spare/parts motor sitting in the garage, waiting to get a rebuild)!
I also have both autos and a stick... the stick is stock, no tunes, and only mods are intake and straight pipe'd the exhaust... feels slow, and it probly is, but it pulls like a bulldozer, and I use it for my main towing/daily driver truck. The Excursion and the yellow dually both have tuners and are quite quick for as heavy at they are. However, they are not drag racers, but fun daily drivers...
Reading your post, it sounds like you may be concidering any model of powerstroke, as in the 7.3, the 6.0, and maybe even the newer 6.4's or 6.7's... I can't give any feed back first hand to anything other than the 7.3's, but they are not the fastest ones for sure... but will run for along time with basic maintnance, we have 253K on our Excursion, and over 300k, 400k, 500k miles can happen.
I have been very happy with my yellow truck, bought it in 2007 with 143K on it, totaly stock. I did an intake, straight piped the exhaust, put in some gauges, and installed a DP Tuner with an 80 hp economy tune. It's heavy, about 9k lbs, gets about 12 to 14 mpg running WV hills and country roads, and the trans needing rebuild has been the only real issue I've had in the time I've had the truck. It's up to 220k miles now...
7.3's are great, I'll buy every one I can...
'99 E350 DRW Stahl 11' util box van, 7.3 PSD, stock. 138k SOLD
'00 F350 extcab, 9' utility bed, dually 221k
E'99 F250 extcab, S/Bed 211k
'00 Excursion Limited, 7.3PSD 281k
'84 Chevy K-30, 6.2L TD, woods/trail beater. 141k