Since the beginning, I've always run Dexron ATF in my tranny. Been thinking lately... I know the fluid must be a GL4. So, instead of running the heavy 75W-80, or the ATF, what would the effect be of running, say a straight 30 or 40 weight engine oil be? The only reason the I'm considering a change is that my tranny, being an 18 spline and slick shifted, is kinda noisy on the street. Lately, I've been doing more and more street driving. Thus the noise issue.(or non issue) Thoughts???