Switching from hotshot to Flatbed

[Chamberpains]

I personally wouldn't eliminate it for that fact alone. But I would be taking my laptop and Insite to go have a good look at its history myself. 4300 RPMs is extremely high. It's tough to get it up there you would have to be coasting downhill with the clutch pushed in while it's in a lower gear and then just let it fly. Or yes it could be simply a sensor or signal problem.
that ECM print out look like a typical company truck. It may have been abused by dummies but then again how much was it abused? That's the question with all used trucks. Has it been in framed or overhauled? That could explain that RPM recording too. Maybe it came apart once.
If I remember correctly The lifelong average fuel mileage is in the 6's but it's up in the 7's since the last ECM trip reset. So maybe it was driven a lot lighter later in its life. All questions you have to investigate and look into.