holley carb help,transition/stage

.075 to .069 in IAB is a good sized jump. Enough that if that's going to effect the problem condition it should be noticible.

As far as the secondary t-slot exposure, someone here may know the HPs and see this.
If not next time the carb is off the engine, see if the secondary t-slots are shorter or located a little higher up in the throttle bores than the fronts.
If so, then opening the secondaries so the t-slot exposure is the same as the primaries means the secondaries are open more than the primaries.
That might be OK or might be something that needs exploring at some point. By exploring I mean reducing the secondary idle position a hair and opening the primaries a hair.

Have fun at the track.