I have a very slow kitchen sink drain and I have snakes it out with no success. Is it possible to have an air lock in the line somewhere. I have put an in line vent in and still nothing seems to be helping. Could I have a blockage in my roof vent not allowing it not to drain. My bathroom sink seems to have the same problem but my toilet and bathtub both drain and flush with no issues. Can anybody suggest a solution.

"possible to have an air lock" no but a clog yes. You may have snaked your drain but just not far enough. If your toilet and tub are working fine I think is more likely a drain clog than a vent stack issue. Where and how did you install an in line vent, guess you mean an AAV.

I installed it about six inches from the P trap and is nine inches above the trap. I also snaked the drain out all the way to the main stack,it's only eight feet from the sewer stack.the bathroom sink is only three feet from the main sewer.