Without any changes to the super-restrictive Greddy elbow and 2" downpipe, full boost at 4500 sounds dead on. I could never figure out why such a small turbo lagged like a 57 trim but had absolutely no balls up top but it does. If you are building full boost, I can assure you that nothing is wrong with the turbo, the problem lies in the exhaust setup. If you upgrade to at least a 2.5" downpipe with a 3" exhaust, I guarantee you can be making full boost at 3500-3800 considering at 4500 feet I was fully spooled at 4000.

If you have the Crome tune available, I would love to take a look at it. That way, we can actually determine if it is a shoddy tune or something else.