Changing out tranny fluids with Amsoil

I have a '96 Tacoma, 4x4 excab, 5 pd Manual, 2.7 lit, 4 banger, 183K miles.
I going to change out the transmission fluid, front and rear diff's. with Amsoil.
I would like to know which fluids you used? Did it make a big difference?
How do you know which transmission fluid to use? There are 2 different types GL-4 and GL-5

Thanks

 

Synthetic Universal Automatic Transmission Fluid replaces Toyota Type T and Type T-IV.

From here: http://www.amsoil.com/storefront/atf.aspx

Check out the blue bar at the top of that webpage. It covers all the apps Amsoil covers.

I e-mailed Amsoil once, and they actually answered me! Give them a shout if need be.