So I got my rev problem fixed by changing the dump valve but.....

[Waffle]

The car feels way slower now. The bov is used and is branded 'forge'. Can this happen?

 

[Evomad4]

dump valve could be leaking under load. so instead of the dv staying shut it could be slightly open due to the spring being to weak

 

[DDS789]

As evomad4 has said

Or some form of boost leak.

The easiest way to test is to take the DV off block the holes and the vacuum pipe and take for a spin if all power is back then the DV is to blame.

What car was the DV off?

 

[Billy MR]

Also some dump valves needs mapping to the car