[Butterman]

I know it's been a while and I'm not sure if someone's told you since but rods snapping under deccel at high rpm is very common for a couple reasons. So by looking at your rod it's clear that it failed under tension, because it's torn in half and not bent, which indicates that it failed during deccel.

There's a compounding issue here. When you're decelerating the tb is closed so when your intake stroke happens the piston can't pull in fresh air and instead pulls a vacuum which causes a tension force in your rod. This combines with the tension forces in the rod caused by the centrifugal force of spinning this whole chunk of machinery (this force exponentially increases with rpm). At the same time these forces stretch your rod and actually reduce the cross sectional area of your rod. Which means less material to support the increasing forces aka an increase in stress.

Unless you had pinging/detonation which previously damaged the rods then this probably had nothing to do with boosting your car, this could have happened to an NA motor. In fact, this shows that your tune and boost weren't the issue.