general problems of the 2002 Ford F-450

In August of 2007 5 of the 8 ambulances in our municipal fleet began to stall and loose power and not be able to get over 35-40 mph. We found the fuel filters full of silver flakes. After removing the fuel tank we found the lining of the fuel tank flaking off. Even though these units were out of warranty Ford paid 50% to replace the tanks, fuel pumps and sending units. Today 2 of the same units began to experience the same drivable problem. This time we found rust particles in the fuel filter housing and the filter plugged with these rust particles. After removing the fuel tank we found the bottom half of the fuel tank completely covered with rust. These units never get below a half tank of fuel. We have tested our diesel fuel and the samples have come back from the lab normal. We also replaced the filters on the other 3 units that had tanks replaced last August and found the filters plugged with rust also. We have a total about 40 diesel vehicles in our fleet and these 5 vehicles are the only ones experiencing a problem. We cut open filters in other diesel vehicles in our fleet and found no problems. This presents a safety issue with vehicles that potentially could fail while transporting patients. The affected vehicles are 2002-2003 Ford f40 with 7. 3 diesel engines.