After changing my brain box of my SUV,I start experiencing hard start in my car

Possibly the learning curve of the new computer. you must drive the vehicle around in certain conditions based on manufacturers specs. drive the vehicle for about a half hour some wide open throttle for a few where allowable and steady highway speed as well. theres a learning curve as called that the computer must go through in order to calibrate the engine.

ECM Learning Curve Dodge Cummins Diesel Forum ecm learning curve Google Search theres an example.