I got a new RME UCX II audio interface recently which comes with a powerful audio measurement software called DIGICheck. The image below is the spectrum analyser in DIGICheck.
This patch I have a HPF/LPF engaged on the GTCore.
I'm not seeing any tone suck when the GTCore effects are switched off, and as you can see, the Effects Bypassed and the Direct Signal - J 48 are almost identical. I can't explain what you're experiencing. Furthermore, tone suck is pretty subjective. Even playing style can effect tone. Could be you don't like the GTCore? Which is understandable. A lot people don't connect with this unit.
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