Some Ford diesels (not sure about the 7.3, but for sure the 6.0) have had problems with south of the border fuel. Very hard on the injectors. Not sure you can have them checked easily (they are pretty buried in the heads), but it would be something to remember and prepare for. My 1999 7.3L has gone 85,000 miles without a single engine repair - in fact the total repair bills from new for the truck stand at about $280 (rebuilt alternator, new pinion seal). The cam sensor was replaced as a recall, but had not failed.
