67 Fury Motor Questions

I have two questions:
1. I changed the oil in my Fury. When the car is idling the oil light flickers but as soon as you give it gas it goes away. So everytime I come to a stop the light just flicks on and off. What could cause this?

2. I was on the highway tonight doing about 65mph. I kicked it down and a big billow of smoke came out the pipes. What could cause this? Bad seals?

Thanks Guys.
Author: furyaboveall