'01 Express 3500 high idle

I have been haing high idle problems for quite a while. I replaced the IAC and TPS and the problem went away. Within 6 months the problem was back and so I replaced the IAC and the problem went away again. Now it is only 4 months later and the idle is back up. Any ideas as to why the IAC keeps going out? I am thinking that there is something else wrong that is wearing it out.

Have you looked for any vacuum leaks in the area of the TPS or IAC. Possibly a bad vac hose that you reconnected when working then worked itself loose?
Just a WAG. Possibly an electrical connector that was marginally connected that you bumped and reconnected while working and then worked itself loose again? Have you scanned for codes?
FWIW
YMMV