I just put a new engine in my 09 CTSV. As far as I know, there were no issues with the trans prior to the new engine. The trans shifted great. Now with the new engine and additional mods, the car is intermittently slipping part way through second gear. It happens when I floor it in second gear at approximately 40 mph. All the other gears and shifts feel great. (1st gear unknown as of now due to traction)
So I double checked the fluid which was full and did a fast learn on the trans. Now after the fast learn completed it slips in almost every gear during the shift at part throttle. the RPM's would flare up and i would have to let off the gas to let the next gear engage.
Any idea what my issue might be?

