Exhaust Popping on deceleration/downshift

Took the car to Wakefield Park last Saturday, I had some issues on the track and see if some of you can give me some advice.
Car: Gen3 SW20 3SGTE 
Mod: Standard built with de-cat dump pipe & exhaust
 
1. Exhaust made some loud popping when I decelerate (from 4th gear back to 3rd) on the high RPMs
2. Similar to above, when I downshift from 4th back to 3rd gear down the main straight, the back of the car tilted/twist a bit and few times that I almost lost back tractions.

.1 sounds normal... And possibly sick as fark if there were flames involved

My gen 3 occasionally does a small backfire under certain deceleration situations on the street. Only a small pop though and I don't think any flames come out. 

Thanks guys.

FYI, I spoke to an expert (race driver) and he suggested heel & toe/ double clutch while you decel/downshift on the high rpm to avoid both problems. Looks like more RIGHT foot skills needed for track race! If still popping then could be timing, spark plugs, exhaust leak, vacuum leak etc.