Run a filter on the fuel as it comes out of your secondary tank. Are you dropping out of the aux tank to the main tank and then the engine or pulling straight into the engine from the aux tank? Put a 10 micron filter setup coming out of the tank, run a good treatment that will keep things cleaner as well. Metal tanks in the back of the truck can condense when baking in the summer sun. Make sure the fuel is treated and that will go a long way.