1970 CUDA - 6.4L GEN III Engine SWAP - WOT Issues

Hi everybody. I'm writing here looking for some help.
I installed a 6.4 GEN III Engine (SRT 8 392/485 HP 6.4L Gen 3 Factory Assembly Line Engine - Bouchillon Performance Engineering) with a Computer Management Kit in my 1970 Cuda, all brand new.
The engine starts and idle fine, but as soon I try to accelerate to WOT the engine couldn't hold the RPMs and comes down, when I try to accelerate againt it hessitates. It looks like a fuel cut or lack of fuel pressure, but the fuel pressure is 60 psi constant.
I checked for DTCs, but none is present.
Does anybody here have a similar issue and could help me with some clue where to start?

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