iv got a 2010 super crew xlt with the 3v 4.6 I noticed after I got my exhaust done (replaced stock muffler with flowmaster) I could hear the engine surging up and down at constant throttle in over drive at about 40 to 45mph. It’s not much maybe 2-300rpm. It also only does it in overdrive. It’s not the coil packs or plugs, it idles smooth as glass and revs through the gears smooth, it’s only in overdrive (6th gear) that it happens. I’m wondering if it could be the TPS. I can also feel it accelerating and decelerating as it’s doing it so it’s not the trans slipping, it’s definitely throttle related......any help would be great!!

10k miles on new plugs and new motorcraft coil packs

yep it was all done at the ford dealer for its 100k service