I drive for an owner and he uses synthetic oil in his van.At one time I was a mechanic.Anyone out there who uses synthetic oil in their vans,is a 10000 mile interval too much for this type of oil,I was told I didn't know what I was talking about? The dealership told me no more than 6000 miles!! Also I have put 60000 miles on the van,since Jan 2003 and the place where he has the maintenance says the transmission fluid is ok,at what interval should the trans fluid be changed with the weight we carry in a 3500 chevy van,this seems too extreme? It's never been changed since December,But is very light pink? Thx x(