At that speed, I wouldn't be sure. The Titan has a known 5th gear flat/jerky spot at about 45MPH; I've had two of these trucks and both had the same thing - but I've not heard of any problem like that at +60MPH. As for transmission fluid, get it straight from the dealer. It's not cheap. I think I paid almost 10 bucks a quart last time I bought it. I know there's a few people on here running Amsoil or Royal purple but for my money I wouldn't trust anything but dealer spec on something like a transmission.