05 Columbia Throttle Dieing, speed decreasing.

Get yourself to a dealer freightliner or a company shop. If anything a TA might help.

You need to have a code from inside the engine or at least a set of symptoms that can be traced to root cause.

A situation I could think of would be that you ran out of fuel in one tank and the other is not opened due to a recent service perhaps as happened to me once. Another would be a failure in your intercooler line to the turbo or a leak somewhere along. A third would be a gauge such as oil pressure dropping down lower and lower indicating a leak of engine oil internally into your cooling fluids inside your engine. Many things are possible.

Only a shop can tell for sure. Having a internet diagonise for you is pretty much speculation.

 

Ugh. I hate it when Mr Murphy declares no issues when the wrenches take a look at something.

 

What kind of fuel lines do you have? Kind of sounds like a fuel line collapsing on the inside.

 

What were the inactive codes when it was plugged in?