Bob McGraw - K4TAX
I would check for warm PL-259 connectors. Make sure to snug them with 4" Channel lock pliers. Finger tight is not good enough. And any PL-259 which is warm along with the coax jumper is suspect. Follow this all the way to the vertical. I use a $29 laser IR thermometer purchased from Harbor Freight to make such measurements.
Item 3....seems that a bit of RF is getting into the system somewhere. Maybe due to SWR increase. Again check all connectors and connections in the RF and ground system path.
I have seen some slight overshoot with my K3S when driving my KPA500 with 20 to 22 watts. In watching the PWR LED's on the KPA500, it indicates things run along at 400 watts and then an occasional 550 to 600 watt LED flash. Haven't been able to exactly nail down why. I'm using an Iambic paddle and the internal K3S keyer running 15 to 20 WPM. I've tried both configurations, ALC from the amp being active to my K3S and ALC from the amp not active to my K3S. Still no conclusion.