Performance Degradation 7.4x to 7.6.7

Any Ideas why the system slows after upgrading to 7.6.7?

Performance testing 18 October version 7.6.7 on production server local host (After upgrade 7.4x to 7.6.7)
Open Account Detail: 18 seconds (first time)
Proforma PO Menu Option: 8 seconds (first time)
Select Account Menu Option: 18 seconds (second time selected)

POOR PERFORMANCE, SO ROLLED BACK to 7.4.1 AND RETESTED:

Performance testing 18 October version 7.4.1 on production server local host
Open Account Detail: 7 seconds (first time)
Proforma PO Menu Option: 3 seconds (first time)
Select Account Menu Option: 3 seconds (first time selected)