Davis recorded 13 total tackles this season, with his best game coming against Clemson, when he tallied six tackles in Boston College's loss.
Penn State turned the ball over 25 times in the loss.
Gilliam will rejoin Jim Knowles and Anthony Poindexter Jr. with the Volunteers.
Schlaffer left the program midseason and was the first to enter the transfer portal.
Penn State will look to rebound from a 7-9 2025 season in Treanor's first year at the helm.
Alrbight did not appear in any games for the Red Flash in 2025.