Turbo RX1 will not rev past 7k

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As title states, sled will not rev up past 7k. I have replaced donuts last year, sled stalls when exhaust is blocked. When it hits 7k it will sputter like its going into a revlimiter like launch control, or kinda how a car sounds when it has spark blow out from a turbo.

Sled is an 05 RX1.
turbo kit is the one that mounts in factory muffler location. sled runs good and revs nicely till 7k.
First time with a turbo carb'd machine.

Any insight? TIA