Reply from Pat Burrow (Lubegard):

"Hello Bob --- MERCON and MERCON V are very similar in their requirements. With the retirement of the MERCON ATF specification in July of 2007 Ford will recommend the use of MERCON V for all vehicles now requiring MERCON. The viscosity requirement for MERCON and MERCON V are the same. Viscosity requirement at 100° deg. C for both is 6.8cSt or higher. MERCON SP on the other hand has a viscosity requirement of 5.5-6.0 cSt at 100° C. It is a thinner ATF than MERCON or MERCON V. There is no way a single ATF can meet the viscosity requirements for all three types of Ford ATF. This isn’t the only difference but this is one difference that is the easiest to compare when you examine the physical properties information that should come with the fluid. --- Pat"

Another opinion that the specifications of Mercon, Mercon V, and Mercon SP CANNOT be met with a single ATF!!! The cSt spec@100C on Amsoil ATF is 6.8, which meets Mercon, and Mercon V, but DOES NOT meet the Mercon SP spec, which is required by the torqshift tranny!!!