If the reports are EXACTLY alike, meaning all same accounts, dates, balances, etc., your score would still vary. The scoring formula between EQ and TU differ. However, if exactly alike, it shouldn't vary by more than a few points.
Cdtotten brings up a valid point: look at both of your positive and negative factors listed on pages 2 & 3 of your FICO reports. While the pos/neg facts will differ because it is a different formula, if the reports are EXACTLY the same (mirror image), there would be some consistency and that would include utilization, AAoA (if listed), length of accounts, balances, etc.
The next page to look out for is the Credit At-A-Glance page. Look at the balances, inquiry count, account totals, accounts opened in past yr, accounts with balances, CAs, PRs, lates, etc. All of that must be EXACTLY equal if you are looking to reconcile this score change.
Finally, look at each individual account. Make sure that all the accounts are the same on both reports. Make sure the balances, CLs, "open dates", statuses, worst delinquency, and others are EXACTLY the same.
If any of the above are off, then that can easily explain your score difference. If any of your accounts listed on TU, for example, are older than EQ, then one score could be higher than the other...easily, especially if AAoA comes into play. If lates, if applicable, are on one but not the other then that can easily explain a difference too. Differences in balances or CLs can throw off utilization and that can explain a difference too. If obvious differences like collections on one but not the other, or good accounts on one but not the other exist, then that'll greatly throw off your score.
Finally, even if an exact mirror image, and everything is the same, then understand that there are minor changes that can throw off one score but not the other. TU for example dislikes over-the-limit balances more than EQ. EQ hates new accounts more than TU. TU doesn't like collections as much as EQ. TU tends to penalize for haing fewer $0 balance TLs more than EQ. These are in my experience, anyway. Also note that your EQ may be in a different scoring bucket than TU. That can easily throw off a score.
Starting Score: 627 EQ, 621 TU - 11/15/08
