Sullen made the decision after an official visit to Auburn over the weekend saying "War Eagle" and that he will make the trip across town to play for Coach Gene Chizik.
Sullen notes that he has been recruited by the new Auburn staff since three days after Chizik took over as head coach.
Currently 6-5 1/2, 340 pounds, he is coming off an outstanding senior year for a 12-1 AHS team. He said he is excited about his commitment, but notes it will be tough to tell Southern Miss he has changed plans.
"I was happy at Southern Miss, I really was, but...," he says of the chance to play for the Tigers. "I really liked it (Southern Miss), but it (Auburn) is home and after my mother got sick I didn't want to go too far."
Commenting on Auburn, he adds, "They said I could come in and compete early. I was planning on competing anyway so it is great. I have a chance to play early as a starter in the SEC so you really can't beat it."
Sullen had a good junior year, but dropped weight and improved his quickness and was outstanding at left tackle as a senior. Auburn High coach Tim Carter says the play of Sullen was a major reason his team posted a 12-1 record.
Sullen notes that dropping weight made a big difference for his senior year as the AHS Tigers didn't lose a game in the regular season and the only setback was a third round loss to 6A state champion Prattville. In crunch time, they ran behind the big left tackle.
The lineman was recruited by Tommy Tuberville's staff, but did not get an offer. That changed on Monday when he was told that an offer was waiting for him at AU by the new coaching staff.
"I was very excited," he says of the scholarship offer. "The first SEC offer just happened to be my school."
Sullen notes that he also grew liking LSU, but left no doubt he is thrilled to get a chance to play for Auburn.
"It went great," he says of his official visit. "It was a great experience for me. It was a fun side of Auburn that I hadn't seen yet.
"It was like a completely different world," he adds, noting that he bonded well with the Auburn players. "It was great."
He notes that he never gave up hope he would get an offer from the Tigers even though the former staff had decided not to offer after recruiting him over the spring and summer.
Auburn still hasn't announced who will be the offensive line coach. "They said he should be named soon," the offensive tackle says. "I am pretty sure he will just fit in. He will have to with the new staff. I loved the new staff. Everybody is so down to earth. It was just great. You got a good family vibe and everything."
Sullen's player host was offensive lineman Byron Isom. "We went to basketball game," Sullen says. "Basically, we just hung out with the players to see what the real Auburn and football players' life is like."
He also talked to academic personnel. Sullen notes that he has a 3.4 grade point average and is interested in majoring in mechanical engineering, but is also considering wireless engineering.
The Auburn High standout says that new offensive coordinator Gus Malzahn talked to him about where the Tigers plan to play the big lineman. "Coach Malzahn says of now he sees me as a tackle, but that could change," says Sullen, who adds that he is just interested in playing wherever the coaches want to use him.