Tranny/Diff Fluid Change

Ok well im looking at changing my fluids, and i have a few bottles of Redline 70w-80 and 75w-90. Now is it bad to mix those or is ok to mix those. Also is it bad to run 70w-80 in the rear diff?

It's not a good idea to mix grades from what I've heard, but it's DEFINITELY not a good idea to mix brands. seeing as you have redline though, it might not be too too bad, it'd just make like a 72.5w-85. as far as the rear diff, it's all 70w-90 or 75w if you want. I wouldn't go 80 just because I swear by the manual, but if you live in an area that doesnt get to 100 degrees in the summer then you should be fine. I just swapped out my diff fluid and went with synthetic 75w-90 front and rear, and it's awesome!