It is your money, but unless you have the truck tuned there won't be much of an improvement,

 

Not trying to turn attention away from the current topic, but after reading this thread it has me a bit worried after ordering my SC cortex tuner earlier today. I bought it with the intention of runing the 91 perf tune with 93 octane. All we have here is 87 89 and 93. Am I going to harm my hemi by running 93 octane with the 91 perf tune?

 

It's not a tuning issue. It's a compression ratio issue. You are talking changing pistons and major work. The cost and labor involved in engine work all so you can buy fuel that is a little less money would make no sense at all. And again, you can't run leaded fuel in a modern engine like the Hemi because of the O2 sensors and cats. in other words, it's impossible.

 

You want to run 93 on a 91 tune. Your SC will reprogram your parameters and your engine at that point will call for a minimum of 91 octane to prevent knock. So yes use 93.

 

I have 3 vintage aircraft and I mix the 100LL 50/50 with autogas due to the high lead contact and the low compression of my aircraft engines.
The lead will destroy the o2 sensors and cats and over time will collect on internal components like valve guides and could possibly cause sticky valves. This is common in aircraft with low compression engines running avgas.