Tom: 

I would look at what Alan and Steve suggested. 
I'm a little familiar with the modern kw transceivers and even though you either turn on or off the amp keying circuit on the TS-570, obviously you can adjust the speed on the 590 so I would look at this. 
Remove the buffer and also try the hand mic. Bringing down your carrier wouldn't hurt either as long as you can maintain the rig's full output power in all modes its designed for. 
Again, I can post your msg to Tom W8JI on the ameritron amps yahoo group or you can subscribe your self and post it. 
I'd kind of take advantage of that as you don't find allot of those who were responsible for product development, subscribing to these email lists. 

73: 
Mike VO1AX