I replaced the fluids in my front and rear diff and the transfer case with synthetic. Plus I run synthetic AMS oil synthetic in the engine. I change my engine oil every 10,000 miles and have noticed an improvement of 1 mile per gallon on gas mileage. Some may say that 10,000 miles is crazy but when I get my oil changed the guys can't believe how clean it is. They think it is conventional oil and that I change it every 3,000 miles. I've read reports and have heard that the oils have come a long way. The only reason they say you need to change your oil every 3,000 miles is to sell more oil.

I'm happy with my move to synthetic. Yes it is more money per oil change but less money per year.

I've got 42,000 miles on now and have run the full synthetic for the last 30,000 miles.

Just my two bits.