Reduced Engine Power

[Itsme7]

Hey everyone. Im posting this on behalf of a friend. He has a 05 Silverado 1500 with the 5.3. He recently had the "reduced engine power" message come across the DIC and was limited to 20mph or so. Went away for a couple days and it is back again. He had it scanned, and codes were set for the TPS and Idle speed control. I looked on ebay, and there are parts dealers selling TPS units, but no idle speed control sensor. is this a dealer part? Also, could there be a problem other than these 2 which would cause the "reduced engine power" to come on? He had his check engine light come on at the same time as well. Thanks for the help.