As yall can see, i got a 99 ranger with a 3.0. I just rebuilt the motor in it (from the head gaskets up) myself last sunday, with remanufactured heads, all new gaskets, fresh oil and filter and brand new spark plugs. I have put 400 miles on it this week since i finished the motor. Yesterday i took it to the woods and on the way home today i was drivin down the interstate doin about 85 in 4th gear at about 3500rpms, it went from running smooth to just all of a sudden running like it had a misfire, like one of my plug wires came undone. I checked the wires and there all on good. The check engine light is NOT on. Anyone have any suggestions?

Ps: I have 33"s on the truck with stock gears, so the truck does not have the balls to use 5th gear. So i gotta run it in 4th at a higher rpm.

Any help would be greatly appreciated!

Have you seen this thread? The guy who was having this problem (which sounds almost exactly like a problem I was working on this weekend...) found it was a vacuum leak. Since you've recently done a lot of work, you may have one as well. I could reproduce the "misfire" (or bucking, shudder, whatever you want to call it) symptoms almost every time by cruising at highway speeds on level ground and giving the engine a tiny bit of throttle...just enough to begin to speed up very gradually, but not enough to kick down to a lower gear. Had to leave my brother's house, so I didn't have time to resolve it, but he's going to check it.

like STM said sounds like a vacuum leak, or another trick to check for bad plug wires you can saturate your plug wires (pref' at night, better visual) with windex, the ammonia will cause bad wires to force-misfire..

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I forgot to reply to this post, i ended up pulling all the spark plugs and checkin to see if maybe one of the electrodes got burnt up, and they all looked good. Put them all back in and hooked the wires back up and started it up just for shits and it ran fine. I guess one of my wires were just loose... even though i checked them several times. Thanks for the suggestions though.