Originally Posted by Trav
I am going to change the plugs this weekend. What do you make of the misfire only occurring around 45-50mph? Is there something that the engine does at this speed that would change and cause the misfire?
At about that speed the engine is at a point where it kind of lugs just after it up-shifts. I suppose that's probably intended as part of the engine management (you tend to get the best gas mileage when the motor is slightly lugging). More than related to the speed itself, I think that it's just that any problems become more apparent when it's at that point.
I had the same problem in the truck that I bought and also noticed the same to varying degrees in most of those that I drove. Changed a few coils which made it a better. Changed the plugs which made it better. Changed the phasers, adjusters, etc., which made it better still. Now with the motor running as it should, I haven't had any more problems. Think that it's probably just a question of getting things right overall whatever that might be in your particular case.