[puddleglum]

Okay, I most certainly did misunderstand what this hydraulic regen. system is. Obviously, I have no idea what you're talking about or why you want to do it. None of it sounds to me like anything that will increase your mileage, except maybe the water injection, but that is debatable. When you were talking about pushing and pulling on the brakes and adding a piston into a cylinder, it sounded a lot like you were building an accumulator for the brakes, like the ones I see on heavy equipment. Probably good you aren't, since I doubt it would work properly in an automotive application anyway.
I wasn't saying you shouldn't use the propane bottle. I think it's a good idea. I was just suggesting, if used 2-3 in parallel, you might have all the extra brake capacity you need without all the extra work and expense. I thought you might be able to mount a few smaller ones easier than one big one. Did you check if you have space in front of the rad, between it and the grill. Anyway, it's your truck so go for it if you want. My intent was to be helpful, not critical, just in case it didn't come across that way.