Fine Tuning a 360 Magnum with a Brawler "Double Pumper"

It is not, currently has the stock y pipe into 2.5 inch, flowmaster super 40, then 2.5 back. Basically the stock exhaust just with a flowmaster. I am on Monday getting a true dual with magnaflow 5” rounds with 2.5 inch all the way back if that makes a difference but I’m not sure it really will.

I bumped up the timing slightly and now it has a slight cut out when I blip the throttle again sounding like the engine completely cuts, but it also feels like it has a flat spot when I accelerate.
It will certainly make a difference in how it's tuned. No question about it.