Working on a buddy's truck and having an issue. Its a 2013 silverado. 5.3L with a 224r cam and P.I. Vigilante 3200 converter. Disabled dynamic airflow and running MAF only. Runs great, shifts great, no gear hunting, etc. Only problem is when coasting to stop or braking. Under 40mph is perfect. rpm will flare a tiny tiny bit when downshifting but nothing out of the ordinary. When above 40 mph, say crusing at 60, and you let off the gas to come to a stop, as soon as the truck hits 40-41 mph, the rpm drops off the around 300, timing falls a little bit too to around 14 degrees. Meanwhile, MAP goes up to around 94 kPa and injectors go up to around 11 msec. The RPM will surge pretty good until you come to a complete stop. It was dying untill I added some more base running airflow. That seemed to keep it alive better but didn't do anything towards the surging. I really think it has something to do with the converter since we never had this problem beforehand. Maybe torque management? played with it for a few hours today to no avail.
I tried zero'ing out the TCC desired slip and that didn't help so I set it back to stock. Really not sure where to look.