dad was a mopar mechanic for about 25 of his 47 yrs turning wrenches. it was drilled into the guys heads that went to the training centers for classes that plus 4 was for the ill-fated 604 and for the rh/re trans, as it had the additives mother mopar wanted. does he still do that? no. he used plus 4 in rh/re tans and dex/merc 3 in everything else. hell, he even adds 1 qt of 30 wt oil to his race trans because and old ss racer told him that it helps.