I have transplanted many over the years with great success. I transplanted one to my yard two years ago March, it was 18" then, now close to 15'. It was only 4-5' at the beginning of this growing season, so this was the breakout year.
I pick small trees in the dormant phase, drive a landscaping spade straight down several inches from the stem, rock it back in forth a couple of times, then firmly but gently bull the young tulip tree out of the ground. Then plant it like you would a bareroot pine tree....drive the spade in and make a pocket, place the tree in, then 6" or so away make a parrell pocket and push the first one closed.