This photo album shows how to fix a gasser - I think diesels use the same sender:
http://www.supermotors.net/registry/2742/77131-4
http://www.supermotors.net/registry/2742/77131-4
How many bad fuel gauges have you found on these trucks? I've worked on hundreds, and I have probably a dozen clusters in a box right now, and I've come across one bad fuel gauge head. On most others, it was the SENDER. On a few, it was the gauge face adhesive letting go enough to interfere with the needle's movement.Either way Steve it's the gauge.