my car shutt off on me while driving 99 monte carlo

i have a 99 monte carlos i just replaced the engine a month a go i noticed recently everytime i turned off the car where ever i was going a little smoke would come out i checked what if it was leaking oil but my censor would not say any thing and my liquids where all good. before i replaced the engine in the past two years i had to change the air compresor twice my car locked, i really dont know what it is this time? i drove the car one morning and i accelerated up to 70mph then it shut off on me. Can any one help and has any one noticed the ac system or cooling system on these cars suck? any help from any one? thanks. the car is a v6 and has 75kmiles not many is a new motor, the car has duble moflers and sunroof edition 2 door z edition