Not sure on how these manufactors use "API" in thier verbage. I have seen the test results which sure prove the product is worthy. I can have never had any service issues with products either. My .02
I'll agree with JBoy on the sniff test.

 

The amsoil gear lube is green IIRC, not blue. Minty smelling is also quite a stretch, I'd say foul and sour smelling is probably closer to accurate Even new, the amsoil diff fluid had a strong acrid odor. The stuff I drained out at 15k, which was from the factory, was not brown or awful looking. The smell was very very similar to the new Amsoil fluid, and the factory fluid didn't look bad at all.

 

Same here.

 

The factory fluid almost has a hint of a grapejuice smell. Actually, on some of the D-max sites they refer to the GM synthetic oil as "grapejuice" and like the mopar oil it is way overpriced. My guess is since both GM and Dodge are using the AAM axles there Synthetic fluid is the same thing just labeled differently.