Quick update regarding the H151F: Although it's never had any grinding issues or synchro problems, the 1st, 2nd, 3rd shifts have always been pretty slow and felt "stiff". I ran straight 75-90 through it and a mix of 75-90 and Lucas Oil Stabilizer. Both were about the same, still way to slow and stiff even with a warmed up tranny. Last week or so I replaced the fluid with Redline 75-90 full synthetic
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The difference in shifting was IMMEDIATE. All the shifts are very, very smooth now even when cold and I'm amazed that a switch to a different product could make so much of a difference. Although it runs about $60 (US) to a gallon, I'll likely start running this in every Toyota transmission I currently own. If you're having shifting issues, give it a shot