Ever since I had my new engine installed my car has had an intermittent miss from 1500 to 2500 rpms under part throttle and cruising. It doesnt do it at half throttle or more. Also, whenever it pours down rain the car misses really bad but as soon as it stops raining hard the car smoothes back out pretty much instantly. What could be causing this? The check engine light does not come on for either situation.