Just a thought, But, Have you had anyone check the timing? I would take it to a Good Diesel Mechanic and have the timing checked. There are special tools involved in timing a Diesel that are pretty expensive to purchace. To heck with the Ford Garage, Take it to International or a private shop with a good reputation. Most Ford Garages don't do enough work on Diesels to Stay Proficient where an International Garge does. Hope this helps.

Brad Godkin
1986 F350 CC/SRW
6.9liter/C6