I was just driving through a hilly highway and noticed something weird. I crested the top of the hill and was going downhill for a bit when I glanced down and noticed my RPMs at 3700 even though I was only going 45mph. It upshifted shortly after and everything was normal after that.

So, was that a symptom of the tranny beginning to slip or was it the grade logic doing something weird? I also checked my fluid (it was flushed at 30K miles ago) and it looked brown to me.

 

Its called grade logic. the tranny will downshift/hold a lower gear

 

Grade Logic Control gets a lot of questions on here. We need a big FAQ about all the TL's many not-so-advertised features and characteristics.