2000 Performance Issues...(MVP & SQL Mag, Plz Read)

I am hoping that an extremely experienced SQL Server DBA can assist in this critical matter.

We are in a 6.5 to 2000 upgrade process. Our current app runs in 6.5 with acceptable performance times. However, in our testing 2000 has performed miserably (4-10 times longer for identical processes with identical hardware configurations.) The SQL Server and Windows 2000 server has been configured, according to all documented books by MSPress, for optimal performance. We have reviewed all code that Profiler has helped us identify as potiental bottlenecks in the duration of our largest nightly process. The identified code has been scrutinized by both the development team and dba team using all known techniques in determining indexing, better logical and physical reads, optimal query executation plans and ect.

We are perplexed by having found out that identical, optimalized, indexed code runs the same or in most cases worse in 2000 then in 6.5. Our largest performing benchmark sp's has shown that a process in 2000 runs 2-3 times slower than 6.5.

Are there any undocumented tuning, optimizing or 6.5 to 2000 upgrade issues that can be shared as to why 2000 appears to run slower then 6.5? At this point, it would be greatly appreciated if a highly expereinced DBA can provide ANY insight. If no suggestion can be provided, perhaps a contact or names of VERY skilled SQL DBA's that can be contacted in assisting this problem, whether it is a third party or someone from MS.

TIA