I'm really having a problem with both the pedal getting stiff and it
not shifting as well. It seems to act exactly the opposite of common
logic. It shifts the best after the car sits for a weekend and the
pedal is the easiest to depress. As I drive the car I find the pedal
tends to stiffen up. It's not a huge amount, but it is noticeable. If
the fluid is boiling I could see it not shifting as well, but I would
think the pedal would get easier to depress because it's getting
spongy. On the other hand if my stiff pedal problem was related to the
clutch pedal linkage, I wouldn't think it would change the shifting
only how hard it is to depress. I did try the Valvoline Synthetic
brake fluid, but went back to the GM clutch fluid because of the
lubricating additives.