Thanks for the suggestions guys, I already swapped out both IF tubes. Based on Tom's suggestion I went in and measured the AGC pot and it was jumping all over the place, so I removed it and took it apart. It was clean as a whistle, but I went over everything with contact cleaner and a q-tip, put it back together and got smooth progression of resistance. Once back in the set, no change.
What do you think about those high voltages on 1&2IF tubes? Am I on to something there or likely not? At this point not even sure if it's an IF problem or isn't. I've tried setting my pattern generator for 45.25MHz, which it lets me do. Is that likely to be a reasonable IF signal to test with? It's one of these
https://www.opweb.de/english/company/Philips/PM_5515