DerekW,
Even though I do believe that some of Amsoil's products are of 'high quality', that doesn't necessarily mean that competitors products are second-rate or "Fools Gold", as you call them.
It appears, to me, that the only 'oil research' that you have done is to ask the opinions of your Amsoil dealer & Wade @ NGM Diesel. I don't believe that they are steering you into an inferior product but, that doesn't mean that there aren't other products, out there, that aren't the Amsoil equivilent, or better.
"The 5X40 water Jiffy Lube recommended" is not necessarily an inferior product in comparison with the 15X40. I don't know exactly what brand oil Jiffy Lube recommended but, if you live in a colder climate, the 5X40 'may' be beneficial. They both are 40's, once warm.
On Amsoil's website, their Heavy-Duty Diesel & Marine, 15X40 was $25. 70/gallon. I, recently, purchased Schaeffer's 9000, 5X40 ("Fools Gold") for $18. 41 per gallon. Many consider this product to be of very high quality & verify there opinions with 'great' used oil analysis reports.
Yesterday, I saw Mobil 1, Turbo Diesel Truck, 5X40, CI-4+ for $22. 00-23. 00/ gallon, at Walmart. This is, also, considered to be a quality product & it's readily available.
There are numerous other products, out there, also. I would recommend that you go over to BITOG (bob is the oil guy.com) & do a little reading. You will be surprised at just how many quality products are available, to us. Besides that, you may gain an even 'greater appreciation' for the product that you choose to use.
Joe F. (Buffalo)