Have you tried as I mentioned, ie can you get it to boost above 5k if you don't use wot. I ask because if the ECU is pulling timing and or dropping your boost via the boost controller due to bad AFR or IAT's then don't stress the engine and see what you can get.
If you put the car in 4th or 5th and do some steady pulls you will definitely be able to hear a leak that drops 50% of your boost. Also in 4th & 5th things are less hectic and you will be able to achieve full boost using throttle control.