I'm guessing your using an SCT with it being a Bama tune.
This probably depends on what gear its getting up to before it will no longer shift.
The settings on the Diablo are:
1-2 upshift MPH
2-3
3-4
When you increase these values the autobox only shifts up when it reaches its original MPH + the value you have added. Basically holding the gears for longer, so if this is to high in 3-4 it would take longer (or you would have to be going faster) before it would change from 3rd to 4th.
(Note: this doesn’t seem to affect change down, only up.)
So this is unlikely to be the problem.
The other setting on the Predator is:
Shift point RPM 1-2
2-3
etc
This is only used on WOT. Basically, what ever these values are, the auto box will only change up when it reaches this rpm.
This kind of setting is more likely to be the problem, if its set to high or higher than you can rev then you won’t reach the next shift point and wont shift up (in theory).
Hope that helps.