Stuttering inline 6

[matt_l]

I drove my truck up to the glass shop yesterday to get a new windshield put in, and at about 40 mph the motor would start to miss/stutter. If I slowed down, it would run fine, and then as soon as I got over 40 or so, it would start to miss again. It seemed worse on the up hills, but hard to tell. What should I check? I ran ok when I drove it home last year. Ok, not great then either, but it did not have this problem.