Bed PID way out of whack

[TN Yankee]

Hello. I've recently modified my bed to a MIC-6 plate with PEI, and (fairly) successfully ran PID on it, while still on the original v 91-something firmware from 2 years ago. I say "fairly" because it would overshoot by 7 degrees or so, but then taper down to the set temperature. Tweaking that was one of the gazillion projects on my to-do list; for the time being, I just set it about 5 deg low, and when it overshot, I then reset the temp to the desired setting. The point being, it read the SeeMeCNC thermistor correctly and so I know it's working.

I've moved to v 92.2 in conjunction with adding the accelerator board to my E3D V6 hotend. I changed the EXT0 value to 8, and it works fine. I left the heated bed sensor at the default 97, but got the same results with type 98 (the type in my v91 f/w). The new PID values are considerably different from my old values, and it seems to stabilize at a touch over 14 degrees too high, though it only overshoots by about 3 degrees above that, which is nice. Re-running PID gives me the same results. Plugging my old EEPROM PID values in gives me the same 7 degree overshoot, then tapers down to about 4 degrees too high.

Old values: 20.24 0.25 417.12
New values: 4.74 0.06 89.63

Why did v92 give me such radically different PID values, and read the thermistor wrong? I'd like to be able to run the PID routine from time to time and not be stuck with my v91 values, but right now something is amiss.

Thanks!

[TN Yankee]

Moved to http://forum.seemecnc.com/viewtopic.php?f=77&t=11306.