89 tune

[ttc06]

I'm a new user with a 2012 Ram 1500 hemi. This tuner has made my truck a completely different beast and I can't believe I drove it so long without Diablo.
My question is why there isn't a 89 tune. Can I run 89 on the 87 tune? I'm considering just using the 91 tune but I'm not sure if the extra cost will be justified in mpg increase.

[HemiSilva]

From what I've read they do recommend 89 octane on the 87 tune.