Or where is located so I can check to see if the screws show signs of being removed and if the part looks new or just as dirty as the other parts sorrounding it
The valve body is part of the transmission. It is the rectangular part, on the bottom of your truck, that has the transmission cover bolted to it. (The transmission cover is a black plastic piece, about a foot across, maybe 18" long, 1" thick.)
The valve body is a series of channels for the transmission fluid to port through. Various sensors and solenoids are attached to it, as are some wire harnesses for them. That's how the "brain" can affect the "body" of the transmission. The brain is a chip (TCM, Transmission Control Module), the body is the gears and clutches (The transmission bell housing going back to the output shaft). The valve body makes electrical signals into hydraulic changes (using the solenoids) and reports the status back to the brain (via the sensors/pressure switches). There are check balls, springs, and gaskets and other stuff in valve bodies. A valve body looks like a labyrinth. They're part of the magic of automatic transmissions.
I am not a transmission guy. I have seen valve bodies removed by experts in less than 5 minutes, after the transmission had been drained. (<- optimal conditions, by guys with over 40 years experience doing nothing but transmissions day in and day out.)
It's well within reason for it to have been replaced within that timeframe.