Not sure on the best method to fix it, but if you do go down the path of external boost control - I've been using a Greddy profec II with no issues.
It runs over and above the stock
ECU with no problems at all and holds boost well. Also has high/low boost settings so you can drive around every day on low boost setting and crank it up at the press of a button when you want to hit the track, overtake, etc.