I think your initial timing is still not advanced enough, which causes the backfire and bucking when you get in the throttle when climbing and you lose vacuum. The initial backfire may have caused a leak in the exhaust system, usually the donut at the headpipe. This causes popping when deccellerating. It is also possible to have and intermittant electical problem that can cause backfiring out the exhaust. Did it backfire through the carb when it was bucking?
