When the truck has 87 octane gasoline, it seems to idle a bit rougher than with 91 octane? Also, no matter what octane, when I shut the truck off, I feel a tiny shudder from the engine. Are these normal? I read so many posts of engine and transmission nightmares that now I'm so paranoid!!!!

 

Modular engines idle fairly smooth but not perfectly smooth and unless you’re tuned for 91-octane you should stick to a good quality name brand 87.

Hard to comment on the shudder without actually feeling it. How many miles you got on the engine? Is it broke in?

 

Only 5K miles on the engine so maybe it's not broken in? I'll try the 87 octane and see if the idle changes