IMO, your idle-timing is your problem.
Coupled with, most likely, a partially open Secondary throttle, and Primaries that are too far closed.
There is NO GOOD REASON to run big idle-timing numbers, NONE. People do it to get the stall-timing right, cuz they don't know how to properly modify the distributor. Or, they're just lazy.
BTW, I run a 12.5PV on my 360 with a 276/286/110 cam (230/237@050), and she will idle down to 550 in First Gear(A833) and pulling herself around the parking lot at 5* timing advance. She'll go down to 500 if I ride the brake a hair.
Fix your timing