How to clean truck seats?

Six years of using my F-150 as the tow vehicle has been rough on the interior. The seats are gray cloth and after all the wet boardshorts and towels, there are a bunch of stains.

What's the best cleaner to get these out? I've tried the Tuff Stuff foam and that didn't work.

Use an industrial carpet cleaner and soak, vacuum, repeat - several times. Pre-treat with high-traffic area pre-treatment. Be sure to let it air-dry in the sun for several hours. Do this in the early morning so you have the day to dry. You won't get it like new, but it will be a lot better.