I almost bought a used F-250 from A&W a few years ago. They were upfront enough to tell me that they thought the engine's cam might be 'flat'. Of course, that shot the deal but I admire their honesty in that case and I'd certainly consider doing business with them in the future.
If you're looking for a used truck check out Cowboy Corral on the frontage road east of I-25 by the north Longmont exit (hwy 66). You do have to haggle the heck with them, but they've always got a huge selection of used pickups, acres of used trucks. I bought my '96 F-250 from them a couple of years ago and couldn't be happier with it.