Thank you Bob for the ideas. I just put the K3s into Tune and sure enough I was seeing the usual 20 watts (what I usually use with the amplifier) out on my station monitor so there's not an RF problem with the radio. Yesterday I rebooted the adjunct PC with no change. I haven't checked all bands - I usually operate on 20 and 40m so I need to do a thorough evaluation.

I'll have to look in the parts box for some toroids.