Instead of dropping the dbo.gtseq_thissequence table, try using this SQL as a pre-publish action against the Test Data Repository:
DBCC CHECKIDENT('gtseq_thissequence', RESEED, 0)
The last parameter is the new "reset" value for the sequence. In this case, the next value that the sequence uses will be 1 and so on.
You can find more information about DBCC CHECKIDENT command at this link: DBCC CHECKIDENT (Transact-SQL)
Also, I confirmed with Grid-Tools that they do not have any other official solution to reset sequences at this time. Hope this helps.