I am an AMSOIL guy (dealer too). I have a 2002 Itasca Suncruiser, it is my 3rd motor home and I have used AMSOIL 10w30 in all three (454, 460 and this 8.1L engines). As a retired Army Maintenance Officer I learned a long time ago that synthetic oil was the way to go. My experience has been the the engine runs cooler, quieter, with better gas mileage and with the extended drain interval of AMSOIL (about 3 times longer than normal oil) it costs less. I use it in all my vehicles plus my lawnmowers. On the RV, I use a larger oil filter that holds 2 qts. I too add a quart about every 5,000 miles.