So I read that hardtopguy is where to go for the diff fluid. Is that stuff actually good? I mean.. I don't really have that high performance of a car and what not.. So is it necessary? I know I need to drain and re-fill.. so is this stuff good? (Looks pretty cheap too! )

 

If you are talking about the LE 607 fluid for the rear diff, then yes, HTguy sells it but so does the S2Ki marketplace store, which is based in Cali. Shipping might be a bit simpler.
Having just seen the thread where some oil analysis have been posted, the LE has proven to be an excellent diff fluid, but so is Mobil 1. Whether or not LE is the "best" is yet to be determined.