If i remember correctly GM recommended putting the tabs in the lower hose and not the radiator on the 4.6 North Star.I don't know if this applies to all GM cars but it may have something to do with radiator clogging.From what i understand the GM pellets are the same formula as bars Leak Gold only in pellets,maybe some here know more about that,anyway Ive been running GM pellets in the 99 Caddy now as per GM specs for 150k with no issues,nothing clogged.