I was doing some searching on the internet and came up with this website describing the high idle control for the LMM engines.

http://www.scribd.com/doc/29529217/PTO

I hope this helps someone with this option.

I will be trying this tommorrow morning on a company truck to see if I can get it to work with my Tech II. I will post further of my results.

I think you will find this only applies to 4500 + trucks, but it will interesting to see if you can make it work.

The high idle option UF-3 can be added by the dealer after the fact according to GM, but I have not seen anyone that has actually had it done.

Here is an exhaustive thread about it...

http://www.dieselplace.com/forum/showthread.php?t=350902