it might feel down on power due to the turbo will stop spining with out the dump valve so you will have to wait for the boost to build back up

with the gay valve the turbo keeps it rpm so will feel different

the turbo loosing its rpm id down to the compressed air hitting the tb and bouncing back till it get to the turbo causing it to stall

i may be wrong as ive not seen the car before your problems or after but has happened to me before going from gay valve to no gay valve