Sounds like you may have a leak somewhere to be honest. It is also possible you are over volumed with both cylinders, which would not make much of a difference between the tests.
I also want to point out that you changed the piston as well. Try testing it with the G&G stock piston in both set ups, how you had it first. Piston weight also effects the fps of the bb, and works with overvoluming to effect how fast the bb is. That's something I didn't really touch on in the OP, but that's why you want heavy pistons for DMR set ups.
I broke my gun!