I have a 2005 F350 Lariat excab SRW which I bought used 10 years ago.The first thing I did was get an Oasis report from a Ford dealer,at the time they were free you just need the VIN no. This will tell you everything that was done while the truck was under warranty by any Ford dealer.If there were a lot of issues with the engine more research is needed or walk away. If you should decide to go forward the first thing you need to get is a Scan Gauge to monitor your engine. These cost about $125. With this gauge you can monitor the difference between your coolant temps. and your oil temps. This is the telltale sign for an oil cooler that is getting clogged,you don't want to be over 14* difference (AKA delta),This should be taken as you cruise down a flat road at operating speed.If you have your camper on back and are pulling a hill you will not get the "delta" that you want no matter if your oil cooler is new or if it is 10* out,that is normal. You can also monitor the FICM (fuel injection control module) which Ford says should be between 40-50 volts,I think the average is 46-48 volts and If mine went below 46 volts I think I might get a new one. This is one of the things that can kill the injectors.You can also check your EGR or the charge from the alt. and many other things,all you do if program the thing you want to check.
But as said before the most important thing is MAINTENANCE.
I have never used an oil additive or synthetic oil,have sent my oil samples to be checked every 10K or so miles and they come back stating that I could go further on the next change which I never do,I use Delo LE 15w-40 only and have been since I had my 97 7.3. I use fuel additives intermitently.I have had no major problems with this truck.I did take it in for the "Hanging drop of oil" that never seemed to fall just before the factory warranty ended and they pulled the engine and resealed the oil pan. But before the warranty expired I bought the extended warranty that was offered at the time for $2000 thinking what everyone else thought about these engines. And just before that expired and since I hadn't had to use it I took it in complaining about oil leaking between the heads(In reality it was no more than you would see on any engine,just enought minor seepage to collect some dirt) they had to pull the engine again and at this time I had ARP had studs installed (had to recoup some of the $2000 for the extended warranty:)) I would not hesitate to buy another 6.0 if everything checked out ok.They all have there own problems Dodge Chevy and Ford and they all have remedies. If you get one here are a few things to remember:
1: They don't like to be "chipped" if you do you HAVE to get gauges ie;pyrometer etc.Scan Gauge does not have that capability.
2. They liked to be driven/worked,the turbo can rust up if left sitting to long.
3.Maintenance,maintenance,maintenance.
Sorry if this was long but I could go on.
2005 Ford F-350 ex-cab Lariat 4x4 srw 6.0 Powerstroke
2008 Bigfoot 10.4