I would say you have a problem with the closed loop not falling, ie not cancelling out and leaving a lean cruise mix when it should not.
Closed does not work all the time, like accelerating, high speed/load etc.
If these go too lean the ECM will detect a stall about to occur and raise revs, check your CO at idle, which will NOT BE IN CLOSED LOPP AT IDLE anyway, at least it should not be.
STU is a very very clever chap and knows what he is doing without a doubt, so it might also be wise to seek his help, but I would check baseline CO, set at around 2- 2.5%
tabetha