I did another comparison test (of sorts) between Stanadyne and Marvel Mystery Oil on a recent run out to Albuquerque, unloaded. Kept to the speed limits both ways, ran Stanadyne on the fillup going out there and MMO on the fillup coming back.
Left DFW area on fresh tank with Stanadyne added, filled up at Ft. Sumner NM with 575. 5 miles elapsed, 28. 645 gal = 20. 1 mpg. I put MMO in the tank at that point, and went on to Albuquerque. On the way back I drove through Amarillo and filled up in Tulia, 527. 1 miles elapsed, 24. 297 gal = 21. 7 mpg.
Driving conditions and speed limits were pretty close each way, on the way back I had more interstate driving at NM's 75 mph speed limit than on the way in, but I also took a couple of detours along the way so it should have balanced out. There was altitude gained going west, so coming back was "downhill" a bit but not enough to account for the difference I suspect.
The truck was peppier with MMO as evidenced by highway merges and such, I noted this fact on my IPAQ computer that I log this sort of stuff with (yeah I'm a geek). I have no idea why MMO would make a difference, it is probably just kerosene but my truck seems to like it. Maybe it just likes the taste. Or, maybe the Stanadyne cleaned out the injectors good on the first tank and MMO made no difference at all on the second
Interestingly though, many of my tanks with Stanadyne have actually showed a mileage decrease compared to the plain fuel tanks before / after. Power Service additive does not show this mileage decrease. Just reporting what I've seen...