On my 04 2500hd 4wd I discovered that GM has now decided that we don't need to change our fuel filters until 100,000 miles. The actual filter is in the tank, I'm not sure what it looks like or if it's just the pump sock. I think 100k is a bit much for a fuel filter. The one in my wife's car is absolutely filthy after 30k running Chevron, Shell & Texaco gas. Is there a way to add an external filter somehow?