I agree. I wasn't sure if you had it dumping to open atmos. If you do, you will know it's open cause it'll sound like you have an exhaust leak (cause you do).

An odd possiblity is that your cat is clogged (if you have one). I know sleeper had his turbo on for a while and it stopped spooling. He took his cat out and ran open downpipe to check it and it spooled again.

It doesn't sound possible since your old turbo was spooling fine, but it could be? Just thowing it out there.