I did the 24x conversion on my 99 5.7 Vortec over the last few days and about a minute into driving I get a flashing MIL. Doesn't feel like it missing and all gauges are ok. I started with a stock 01 Silverado 5.3 tune and changes all fuel, airflow and spark tables to my old 5.7 tune. I left the dwell table alone though.
Any ideas? I was logging when it happened if that helps.