I would consider switching over no later than 6th. Thru 5th was fine on ALEKS and with two small exceptions, he was fully prepared for 6th on EPGY. When he switches from 5th to 6th in ALEKS, the pie will come up 80%+ complete. That's what spooked me. When DS switched to EPGY for 6th, EPGY revisited some of the concepts that ALEKS had tucked away in the completed section... and it turned out that DS needed that review (long-division in particular).

Being offended is a natural consequence of leaving the house. - Fran Lebowitz