Chances are that your belts still slipping. I've been down the same road and belt dressing didnt work. Retighten the belts. If that doesnt work then chances its a bad idler pulley bearing. Heres a link to an old thread about the pulley. link


'04 Taco x-cab 3RZ FE stock (daily driver)
'90 x-cab 22RE stock
'82 Hilux 6" lift (ACES HI)
'82 2-Hiluxs' Rally Edition (parts)
'81 Hilux 3" lift (parts/restore)