What does it mean to have devekus to Hashem? Because as you said at the table: You can't think of G-d when driving a car-you need to watch the road. So what is true devekus and what does it look like?
Devekus means cleaving to Hashem. But Hashem is all. There is nothing else. There is no separation between the creation and the Creator. So how is there not cleaving at all times? All is one.
The answer is that cleaving to Hashem means cleaving to the awareness of His Presence. When we consider Hashem as our King or as our Father we certainly can drive a car as our Father or our King would want. But if we are thinking about Hashem as the all and Only, the One Who fills and surrounds everything, then we better not be driving a car or we might go off the road.
Try to recall your greatest spiritual feeling. At some time or times in your life you had reason to be more aware of Hashem's Presence than you usually have. Try to repeat that experience. Try to hold that awareness in your mind for a second or two. If you can, you will want to hold it there even longer. That "holding it there" is your level of devekus. As greater moments come, use them as your spiritual moment to try to recall. From time to time, throughout the day, try to recreate that experience.
When an elevating moment comes look to see what you were doing when it happened. See what seems to be the reason it came, and then have that deed or thought become one of your regular deeds. If it was a significant experience you will want to go stand in the place where it happened from time to time and try to imagine it happening again.
Although the Gate opens from the top down, still we have to do our share to encourage Hashem to open it for us again.