They say your range check should not diminish more than 10% with the engine running compared to the engine off range check.

It sounds to me like you are having an ignition problem. How does it do with the engine not running?

C&H has a tester that you can use to simulate the engine running, it drives the ignition as if the engine is running at full throttle. I think they are only $25 or something like that, I've found it to be a worthwhile tool.

Also, I suggest that you try testing it with a FM (not PCM) receiver. THis will be much more sensitive to problems and will make it easier to identify what's wrong.

Good luck. Let us know what you find.

TF