No power, now won't start
 

Stock 2005 F250, 6.0L, 120,000 miles. I filled up yesterday morning (don't know if it was related, but sure is a coincidence if not), and noticed the engine running rough under ~2000 RPMs the rest of the way to work. When heading home (maybe 40 miles total after filling up), the rough running worsened. Then, the turbo was very loud from a stop (that only happened once - sounded like a semi revving up). Finally, I lost power until I stopped at a gas station after only being able to get up to 4 MPH after a stop sign. I changed the rail fuel filter (didn't have the right size wrench for the engine one), and it started and made it home - less power than normal, and still rough, but I could accelerate. Once home, I changed the engine-mount filter as well. This morning, it started rough and got me out of the driveway before stalling, and would not restart. I'm going to try pulling the MAP and the EGR valve tonight, then check the fuel pressure if they are okay. Any other ideas for things I should check?

Also, there is an electrical connector (brown square connector) hanging by the rail fuel filter. I didn't see anything that it could connect to, but just wanted to see if someone knew for sure; is that just something that maybe goes to the gas models, or is otherwise not used in this truck, or do I have another problem there?

Thanks for your help!

that connector is probably for the fuel heater that they did away with.
The loss of power could be a fuel pump, you can pull the top fuel filter out and have someone turn on the key to see if it fill with fuel, if I does and pretty quickly then you will want to start diagnosing a high pressure oil leak. If this truck hasn't had the STC fitting and dummy plugs replaced in the high pressure system then it very well could be the proble hear.