I just got done today with the 500 mile Auto-Rx treatment in my 98 Ranger.  I was impressed about how it didn't change the way it ran during operation, never overheated, no funny sounds etc..  I also felt confident with it as I have heard alot of good reviews about it at bobistheoilguy.com.  What mainly impressed me was how it never thinned down my oil to a "water like" state as you would associate with other engine flushes that are solvent based.  I drive total 90 miles to college round trip couple times a week.  It ran great, oil pressure was smack in the middle of the gauge and even with the A/C on at times, it ran great.  I was going to use Amsoil in it but for reasons I wasn't able to get it time.  So I went with M1 SuperSyn.  Truck runs great and I will calculate my mileage to see what the increase was.  Great product and I would recommend to anyone without fear. 

Thank you  
Mike