I don't think Tennessee should be nor do I hope that they are. Teams just breaking the top 25 have a very hard time of getting back in if they stumble a bit early in the season. It's the polar opposite of a team that is heavily overrated at the beginning of the year and are top 5, and they can lose 5 in a row and still cling onto a ranking. Yes, Tennessee has a ton of momentum with a good bowl win and an awesome NSD. But in the end this is a team who barely got past Vandy and whose offense really sputtered for nearly half of the 12 games that they played.
Now, if they roar out of the gates and beat Bowling Green big and then roll on OU, then they should be in. If they continue that streak for the next two weeks, then they should be in the mid teens. And if they make it to the Oct 17 bye with one loss they still should be knocking on the top ten. I'm obviously hoping for 7-0 at that point and an even higher ranking as a result (and the east all but wrapped up at that point). However, fact still lies that they play a very tough four games there with one breather: OU -> breather -> FL -> Arkansas -> Georgia.