There are only so many ways to lower the speed. Shorter/weaker springs, lighter piston, sizing the transfer port, hole in the piston face, shorter piston stroke. Without disassembling and taking measurements it is impossible to say what has been done.
I would recommend the Air Hawk. It has a better trigger out of the box. Very easy to work on and being a copy of a Diana 34, after market parts/ kits are readily available.