From my understanding, the F designation is usually reserved for 4x4 versions. There is a 2wd r151 that did not get the super low 1st gear.
Hate to resurrect an old thread but is there an "R151" and "R151F" out there? I know some sites may just not be putting the F at the end of the transmission but wanted to know if there is two different R151's that I should look out for