2nd PowerConnect 6248 in stack is slow

We have a situation where we recently purchased a 2nd PowerConnect 6248 and stacked it with a pre-existing 6248 (~1 yr older), but all of the machines and servers plugged into the older switch have extremely slow throughput (approx 10x slower than on the other, newer switch).

We upgraded both switches to the latest firmware (2.2.0.3, A14) and have dual stacking connections via the 48Gbps stacking modules (Dell part#: 320-5171).

Any help and/or suggestions would be appreciated. Thx!

_Khalid