When you say the Dynamos are draining, do you mean power reserve or steam?
TE Dynamos throttle themselves down based off of how much internal power they have. Basically, when they are making more power than is being used, they will build up the internal buffer. To respond to the lower demand for power, they throttle down to conserve fuel. At 4,000/40,000RF stored they should run at full speed. With a full buffer, you will get 4 RF/t instead of 80 RF/t. So, they SHOULD lose their internal buffer.
Another test of the system would be to set the resonant cell to output exactly 5,760 ( Use ctrl to change it by 5s ) then watch to see if things stabilize. After the dynamos are all drained, you should see the number in the resonant cell pause on an exact number. Then, check the boilers to make sure their steam levels are not going down.