Are the harder shifts going to be harder on the tranny and rear end? I had the back end get loose shifting into 2nd and 3rd. I love it, just want to make sure I'm not going to tear anything up.

I just got the Diablo tune installed on my 2011 Silverado. My primary reason for getting the Diablo is for improved fuel efficiency. That being said, which tune should I run? The guy at the shop said the 87 octane tune is primarily for users in the northern part of the country. Not sure what he ...