Truck was in storage for 2 years

[softballnrd27]

My truck was in storage for 2 years while I was stationed in Okinawa. The guy that was watching it did good in the beginning by driving it and running it every once in awhile. For the last year to year and a half he slacked off. When I had it delivered Saturday I could tell as soon as it was fired up that it was running like crap. It feels like there is a slight miss. I parked it and had to leave for the rest of the weekend. Under the hood looks like it was pulled out of the water, there is corrosion on the alternator and surface mold all over the place. I have new plugs, oil change stuff, electronics cleaner and fuel treatment. There is about 1/4 tank of gas in the truck now, should I drain it and start fresh? The check engine light is not lit when running so I don't think there are any codes being thrown. It has a new battery as well. What else should I do? I will try and get pics tonight when I get home.