boost creep or not
 

I am thinking about getting the FMII kit and adding a 3" exhaust with no restriction after the turbo is that likely to cause boost creep then the only thing to control that would be an external wastegate?
or is boost creep usually caused when large turbos are used to run at low boost?

I have a small turbo and a 3" exhaust and I had lots of creep. I had to port the wastegate.

So how do I stop boost creep from happening keep the 2.5" exhaust? I don't want to open up the waste gate hole in the turbo. What usually causes boost creep?

Boost creep is caused by the inability of the wastegate to divert enough of the exhaust flow around the turbine wheel to maintain a stable pressure reading. Too small a hole in the wastegate and exhaust gasses continue to dump through the turbine passage instead of going around it. Port it, go external, or get a fuel system big enough to handle the airflow (hint: that's the fun way to deal with it).

I suppose that creep could also be caused by a large pressure differential on either side of the turbo, and that going with larger diameter exhaust tubing would add to that effect. But I'm not smart enough to be sure about that :D