I have recently put Amsoil 5w30 in my 99 Camry and 03 Envoy. I bought the XL extended life synthetic and I am wondering how long I can run the vehicles on this oil. I believe the bottle says 7500 miles. Could I go 5000, change the filter, then another 5000, or is 7500 the limit with Amsoil? Any help would be great. I thought I was getting the 25,000 mile oil and was going to go 15,000 with filter changes at 5000, but I ended up with the 7500. I am using Purolator filters if that makes a difference at all. In the past I have used Penzoil Platinum and run it to 10000 miles with filters at 3300 or so. I am tempted to go back to Penz Plat if I can't get more than 7500 out of the Amsoil. I've heard it's a great product, but the Penz is a lot cheaper and is supposed to be a great oil. Thanks