You want the Amsoil Synthetic Universal Transmission Fluid. The other product is if your tranny requires Mercon LV, which is a low viscosity fluid. I don't know the technical differences and since it's not compatible, have no reason to look any further.
I just had my tranny flushed with the Amsoil synthetic universal ATF and noticed a difference (acceleration and shifts were firmer). Didn't do anything for fuel efficiency but unless there's a problem with the tranny, changing the fluid should not make a big difference or have a noticable impact on MPG. Also, Amsoil ATF is rated for 100k miles under normal service conditions so you can go about 2 to 3 times longer in between fluid changes as regular ATF (depending on your belief how long regular ATF lasts!).
2003 FX4 Lariat SCrew, 5.4L, 3.73 Gears, 5" Rancho Lift & leveled, Edge Tuner, K&N CAI, MagnaFlow Cat-back Exhaust, American Racing 17x9 Alum. Rims, 35x12.5" ProComp Extreme A/T Tires