Just saying it was done doesn't mean that the engine is good now. I'm going to ask a bunch of questions and hopefully that will help you determine whether this is a good deal before you spend your hard-earned money. The intent isn't to scare you, but give you some information.
Do you know who did the work and were the heads and block checked for flatness? Why was all this work done? Was it an issue that was allowed to get out of control? Is this a problem child of an engine? Why is the seller selling the truck? Maintenance is key to longevity on these engines and extended oil changes are generally a bad idea. How was it maintained? Are there service records for it? If not, does the seller at least know the maintenance intervals? Also the 05 engine had some problems with the Snap-To-Connect fitting on the High Pressure Oil Pump. There were also problems with the stand-pipes and dummy plugs on the high pressure oil system. It would leak pressure when the engine oil came up to temp-it would drive fine until you turned off the engine; Once you did, you had to wait until the oil cooled enough to build 500psi of pressure in order to fire. Do you know if the STC fitting, stand pipes and dummy plugs were replaced? (If it isn't having a problem, they likely weren't replaced.)