You could go to a Ford dealer and ask them to print you out the OASIS report on your truck...might be able to find a tech on one of the diesel web sites that would be willing as well. That will tell you what work was done on your truck at Ford garages. Obviously, work done elsewhere would not show up, but since the engine is warrantied to 100K, it would most likely be there if there is anything.
Depending on how the PO used it, I'd say it was probably around 40-50k when it was broke in. But, as long as it was maintained properly and not abused, there still should be many more miles of use left in it.
If you want to mod it, just remember that as with most all other things mechanical, the more you ask of it, the better the chances of failure. About the only mod that doesn't apply here is a good exhaust. The engine warranty is just about gone, if it isn't already, so either way, if something happens, it's going to be your dime to repair it.
Head gaskets are a popular repair, but it depends on the truck. Some seem to hold up great, some are just cursed it seems. If the head gaskets do let go, take the opportunity to upgrade to head studs. Most of the reading that I have done says that studs alone with factory replacement gaskets are good to around 450-500 hp. I know mine isn't that high, and probably will never be, but I'll say that for nearly 8,000 pounds of truck, she sure scoots.
Another thing seems to be with the vanes in the turbo sticking. Just as long as it is drivin regularly and every now and again mash the throttle, you should have no problems.
EGR is also a common issue. One of the nice things about the SCT with custom tunes is the EGR can be dissabled, which allows for removal. That will most likely be happening to mine before too long.
Anyway, mine is my DD...I love driving it. I got a stupid grin the first time I saw it, I liked it even better after I fired it up for the first time. Yes, it's big, but for it's size and capabilities, it does get decent mileage in my opinion. Plus, I still like the way she looks and it fits me very well.
I put an MBRP system on it fairly soon after I bought it. I debated for a while on the tuner, but I finally went ahead with a custom tuned SCT. I don't flog the truck all of the times, but it is hard not to sometimes. It really made the truck completely different to drive. Yes, I was conscerned about the engine...and I still do watch it...but so far it hasn't missed a beat. I've never had the first issue with the engine. (KNOCKING ON WOOD)