Allison 1000

Hi Allison Man, I heard that there is an upgrade for the 1000 transmission from a single overdrive to double overdrive. If so, what is it, and how is it done??
Allison 1000

I, for one have not heard of it, but if true, would like to know more. I do know in the 2006 GM trucks there is a + - button on the gear shift. I know it has something to do with manually shifting the automatic transmission. I wonder if this is what you have heard about.