I have been running regular 87 octane (with up to 10% ethanol) gasoline since new thinking the additional octane of premium was not necessary as I don't tow anything and I could live without the extra 10-20 HP.
Just for the heck of it, I thought I would try using 91 octane premium (with up to 10% ethanol) to see what, if any, difference there was. After 5000 miles of using only 91 premium I can say that my shudder issue has been resolved. I have not experienced the shudder for 4 months and the truck runs smoothly under all conditions. Additionally, my gas mileage has increased from an average of 17.4 to an average of 18.3 (according to the "lie-o-meter") with no change in driving habits.
I have concluded that my shudder issue is very likely a misfire occurring under certain load and RPM conditions using lower 87 octane fuel. Yes, it costs me 10% more for fuel but I am getting part of that expense back in the form of better gas mileage. I am really pleased with the improved drivability and smoothness of my truck now. Maybe it is the combination of the installation of TSB 22-2224 and the premium fuel, but the TSB alone certainly did not do the trick. Too bad Ford couldn't have shared this info with me a couple of years ago...
If it is indeed a fuel specification/requirement, then I don't think the fix is going to be easy because it may have an impact on the actual fuel economy rating of the vehicle.
