I have a 99 f550 7.3 that seems to lose power when it warms up. It starts out perfect then as it warms up (about 10 miles on interstate) it will run fine in lower gears but acts like its governed at about 63 mph in road gear. After several miles of this, it will sometimes act like a missing gas burner an drop most if not all power. I can shut it off for 10 minutes and it will go back to the governed thing and can let it cool overnight and it runs like a striped assed ape for about 10 miles and then same thing! I have replaced the in line fuel pump, the ecm, the fuel and air filters, and had the injectors rebuilt about 6 months ago. There is no oil in the fuel filter housing and no apparent leaks. Need some help guys!!!!! Thanks. (Please talk to me as you would a woman! I am a gas burner guy and don't understand all the acronyms so I won't be offended if you treat me like a dumb a..). Thanks again!!!!!

 

Those chassis models with the metal tank in the rear were really bad about the lining coming off of the tank. Once it floats around in the tank, it gets sucked into the pickup causing what you describe.

Its just a guess. You can verify by checking fuel psi as it drives. That requires the installation of manual gauge at the fuel filter housing.

 

How long have you had the 550 honey?

Are you worried about the high rpms and loud engine noise at 63 mph baby?

Sometimes, people who aren't used to the 4.88 gear in the rear complain that it is hurting, when it is really ok. You'll get used to it dear.

(Is this what you meant?)

My 550 turns about 2450 RPMs at 63 MPH if memory serves correctly.

Checking the fuel filter for grey flaky material is also a good idea, but you have already done that, so that would seem to eliminate the interior tank sluffing being an issue.