2000 4.3 idles rough and codes.

2000 idles rough after it warms up and is driven for a while. Changed plugs AC's rotor, cap-- no change. Replaced plug wires one by one with Borg Warners. All went fine and used proper grease. No idle change. Now have service engine soon coming on, with code P-0753 and P-1351. I was told that one is a trans selonoid code and one is an ignition voltage code that only a dealer can correct? Seems that I am making matters worse. Any ideas?