I have a 2004 6.0 diesel.....when pulling a trailer it loose's power going up a long hill.....Any suggestion please?.....I have changed the fuel filter and fuel pump...dropped fuel tank...checked sending unit screen...acts like it runs out of fuel...

 

How's your coolant and oil temps? You need to know this. Do you have scangauge II? Dash gauges don't mean nothing.
Checked for boost leaks? cac tube boots cracked?

 

It could be lots of things get a SGII to start reading things

at a guess bad or dirty egr valve

or at least get codes scaned at auto part store

 

As Benny said, checking for codes is always a wise thing to do (you can have stored codes without a CEL).

Is your 2004 an early model year (ie the ICP sensor behind the turbo)? Check the ICP sensor connector and see if it is leaking oil. Disconnect it and see how it runs.

Also, you may want to check FICM voltage.

There is a low power troubleshooting thread in the Tech Folder.

https://www.ford-trucks.com/forums/9...condition.html