Its more than that. Its too thick to let the synchomesh do its job. Imagine sandpaper covered with thick oil. Sandpaper doesn't work. Same concept. When trans oil gets older people notice it take much much longer to thin out.
Agreed, I should have elaborated. I don't believe in lifetime fluid, especially when I plan to drive my car to high miles (above 200,000), or until it no longer makes sense to do so. So I figured I would change my trains fluid every 60k miles. Since I don't like the RP in the cold anymore, I'm probably going to change it again soon to something different.