Since 1999 only 4 non power 5 schools went undefeated Marshall (1999), Utah* (2004, 2008), Boise State (2006, 2009), and TCU* (2010).
Utah is now in the PAC 12 and TCU is now in the Big 12.
Utah in 2004 played 3 schools that are in the power 5: Texas A&M finished 7-5, Arizona finished 3-8, and North Carolina finished 6-6. Utah played one ranked team #20 Pittsburgh finished 8-4 and dismantled them 35-7. Utah end of season ranked #5/4
Boise State in 2006 played only 2 schools that are in the power 5: Oregon State finished 10-4 and the only ranked team #10 Oklahoma finished 11-3. Boise State end of season ranked #6/5
Utah in 2008 played 3 school that are in the power 5: #24 Michigan finished 3-9, Oregon State finished 9-4, and #4 Alabama finished 12-2. Utah also played two other ranked teams #11 TCU finished 11-2 and #14 BYU finished 10-3. Utah end of season ranked #4/2
Boise State in 2009 played 1 school that are in the power 5: #14 Oregon finished 10-3 and played another ranked team #3 TCU finished 12-1. Boise State end of season ranked #4
TCU in 2010 played 3 schools that are in the power 5: #24 Oregon State finished 5-7, Baylor finished 7-6, and #4 Wisconsin finished 11-2. TCU also played another ranked team #6 Utah finished 10-3. TCU end of season ranked #2