The air preheater, "thermac" system is more for cold-start
driveability. If your engine is having issues after it's warmed up, I'd look elsewhere to recitify that.
I'd be hard pressed to buy new components at those
prices. I'd test what I had, and if necessary, replace what's required from the wreckers (after testing them).
[This message has been edited by Patrick (edited 02-04-2014).]