4000 miles ago I had my engine rebuilt. Everything was running fine and pampered in order to 'break in' the engine. Recently, the vehicle has had a slow acceleration issue. The engine sounds fine, air filter is clean. About 3 times the car's RPM has dropped and seems as if it wants to stall when I come to a complete stop but it recovers within a couple seconds. Do you have any idea of what the acceleration and RPM drop may be related to?