[Jackpine]

I wouldn't bother. I've never used 91 octane gas in my truck and I tow a travel trailer that weighs about 3600# (empty). I've pulled it over the high passes in Colorado (Red Mountain and Monarch, among others) that are 11,000+ feet high with no trouble at all. I pass all the big rigs toiling up the slopes with no difficulty.

On long uphill climbs I lock the transmission in 2nd gear to keep it from shifting up and down. I do the same thing on long downhill slopes to use engine braking instead of wheel brakes.

I honestly doubt you'd see that much advantage in pulling power with a 91 octane tow tune. These trucks were designed to burn 87 octane. I'd stick with that.

I was born near Donner Pass in the town of Grass Valley. Some day I need to get back there.

- Jack