I've previously posted that the original ATF in my Allison was a dark purple from day one. A few others posted having the same color fluid and the thought was there was some bad dye in the ATF used by GM. At @15,000 miles, I drained the pan and refilled with 7 quarts of Transynd. Color remained the same. Now at 30,000 miles, the ATF is black...I'm talking as black as the engine oil after 5,000 miles. Doesn't smell burnt, but doesn't smell right either. Tranny has never seen above 190 on the gauge. I ran 28 quarts of Dex III through the tranny tonight and I still can't get the color back to red. The only "not so smart" thing I've done is run with the grill cover on this month. I installed it in December because it was one cold-a$$ month here. January has been a pretty mild month to date with some days reaching into the 50's. On those days, the engine temp runs about 205 and the tranny runs about 180 - 190 if I run on the highway. I didn't put a ton of miles on the truck running at these temps and they are no higher than what I see in the summer towing. Did I cook the fluid leaving the grill cover on at temps under 200??