Try another ignition module. It is quite possible it is failing. The ignition coil can break down inside easily as they run a higher voltage through it to develop the spark and if the spark gap gets too large the voltage level spikes really high causing the windings inside the coil to short out. A common symptom is you can't rev up, but it may idle though, and it just gets worse and worse as the coil keeps getting worse until it fails completely.

of course one other thought is that the timing sensor on the front of the engine is starting to fail. If that is true then it is much cheaper to get, as they sell them separate on some engine brands and ignition modules.