So, last week on my way to my vacation destonation my truck ran fine untill it hit around 63-70 mph (max speed Ill run my truck) then it would rumble a little bit constantly, and on the way back it did it too (all 325 miles), but last night when I went on the interstate to get madden 09 I hit 63-70 and it ran fine. I was wondering if I just had some bad gas or maybe something finally breaking in since im only at 77773 miles today. I looked around underthere with the motor on and off and nothing looked loose, thought maybe a mount but they're all fine.

I am clueless to what happened, and am worried about something happening soon.