Just wanted to plug Diesel Dynamics for their exemplary customer service. Monday I priority mailed my DD2's to the manufacturer with a comment of decreased fuel economy. They called me today and had already tested and found two bad injectors. Two injectors have been rebuilt and four "shimmed' to meet DD's standards and are on their way back home. These injectors are five years old,albeit low mileage and DD warrantees them for life! I've replaced them with Mach 1. 6's which are a step up but cannot say enough for Diesel Dynamics. Two thumbs up for USPS' $8. 10 flat rate priority mail boxes. Nice to give credit to a federal agency.