The V6 MEMCALs are much more plentiful than the TBI MEMCALs, which is why the V6 MEMCALs are used.

The V6 MEMCALs were used from about 1987 to 1994 in many applications, whereas the TBI MEMCALs were used from about 1992 to 1995, and only in pick up trucks, and not all pick up trucks of those years.