I have been reading threads on this site for advice. The most recent thread I've found is from 13 years ago. If you know of a more contemporary thread, please share a link.
What I have:

• 1996 Dodge Ram 1500 4wd regular cab 5.9l
• Shorty headers
• Very old cat-back system (probably a part of the original purchase)
• Kegger mod and fixed intake plenum gasket
• Gasket-match ported the intake and heads (mostly)
• Opened up the throttle body by removing the bevel (silencer chamfer)
• New wires, plugs, cap, and rotor
• 4-row aluminum radiator
• Rebuilt transmission
• New torque converter

I share this information to minimize the suggestions on things I have already completed. These trucks have many things that need repair/update.
This is the kit I have been mulling over: https://eflexfuel.com/us/auto-products?product=eflexpro .
FIRST QUESTION: What's your experience with a modification like this? Please share if you have performed a similar modification. I understand that E85 has less energy than gasoline but has a higher knock tolerance, allowing you to run more timing and possibly run cooler. I understand it will need more fuel to operate correctly, but E85 (in SoCal) is less expensive than 87.
SECOND QUESTION: Does the cost of E85 outweigh the mileage differences?
I have owned the truck a few years and I primarily use my truck to tow. I am well aware that these trucks do not get great gas mileage, but I am trying to reduce the beating my wallet has been experiencing.
Thanks for your help! =)

 

1000 bucks? I'll pass. Smells like snake oil to me. For less money, you could just get a performance tune for your engine, and be further ahead. Sure, E85 is cheaper than E10, but, your fuel economy also drops like stone, so there is no savings to be had there.