I recently swapped a 2018 L83 w/6L80 into my 1980 C10. I just recently got it wired up to a point of starting. It fires right up and idles fairly smooth for about 30 seconds. Then out of nowhere the spark advance shoots up to anywhere from 30 to 40 degrees. At that time the idle starts hunting and the timing is all over the place. Vats are disabled, DOD is disabled, COT disabled as I have not cats. I have not changed anything in the DTC. What am I missing?

Anyone have any ideas as to what could be causing the issue with the timing?

c10 at idle tune 4.hpl
c10 stock tune - vats disabled - copied from stock 2018 - 4.hpt