Tuning an old Buick with an L98/6L80e combo that constantly cycles between 5th and 6th at 100km/h.
It happens in a very regular pattern.... roughly 10 seconds in 5th, then 10 seconds in 6th and so on....
No BCM fitted.
Speed sensor reads correctly.
I have made ALL shift tables the same, to eliminate any of those issues..
any ideas??

