Okay so my Altima SER had a cracked head gasket for about a year, and about a month ago i was driving down the road and a car was tailgating me so i stepped on it, and i redlined the engine im pretty sure, i didnt quite noitce but all i hear was my engine like blow. So about a week ago i got a new engine installed, it was a 2006 3.5 Maxima engine and my mechanic had to use like manifold and block from the SER engine so it can fit better. My car is preforming better now, finally no burnt oil smoke coming out the exhaust. The car still is struggling, when i step on it doesn't pass 4200 RPM and i hear a lot on engine noise when i drive/step on it. Buddy of mine says it might be the cats, but need yalls opinion.