Open loop in 87 performance tune??

[Chris74]

I know Bill is away and he'll likely confirm this when he gets back.......but does anybody know if our trucks will go into open loop under say light to moderate acceleration. I mean while on one of Bill's custom 87 performance tunes (or even 91 or tow tune).
If so, at about what rpm would they do that? I assume it will immediately revert back to closed loop once you level out to say a 65mph cruise?
I know it's open immediately at WOT but I'm wondering with the custom tune if it opens up at say half throttle.
I'm getting my truck dynoed on Friday and plan to do atleast one partial throttle pull to check the a/f at a light load cruise as well.