Know of several that use filtered vegetable oil from resteraunt fryers. Start on diesel then switch to veggie oil then before shutting engine down switch back to diesel for a few minutes.
Dont know about yours but 2000 RPM is the magic number for mine, if I stay at or under I get around 18mpg on the highway whether towing or not maybe give that a try. With 3.73 ratio and 285/75R16s that gets me close to 70mph.
I just replaced the plug on my cord and routed out between hood and left headlight it's been that way for 4 years now without any more issues, and we use them quite often here in Alaska.