UPDATE:
I haven't been driving the pickup much this winter so I haven't needed much diesel. I've only filled it twice since learning about Mudflap and neither time was it below half. So far, I've saved $27 in only 2 fill ups. I'm comparing the Mudflap prices to Walmart, the cheapest diesel in town. I drive by there a couple times a week. We only have 1 station nearby who's on Mudflap and it's 13 or 14 miles to it from home and it's well out of my usual line of driving. This station isn't the cheapest one around by any means.
