On closer inspection of the Actuator on your web site (Menu#24) the butterfly appears to be at a 90 deg angle to the barrel.
Before installing mine is definitely not at 90 deg (flat). Is it supposed to be?
It appears to be about 88 deg.
There is no change in the angle with and without the linkage and spring attached.

Also

Using gas pedal, engine will increase RPM until about 4100 rpm then it will feel as if missing severely and will not rev higher.

Any thoughts are appreciated.

Bob