Hello Scotty to see if this has been asked before and didn't see it, sorry for the over sight if it was.

I have a 2008 ford expedition Eddie Bauer XL with the 5.4L triton engine and a T6R60 6 speed auto transmission with around 180,000 miles. I love the truck and for it's size it's gas mileage isn't that bad. The one thing is, and I've been trying to find out if this is an engine or a transmission problem. Both part of the power train have been scanned and show no codes. When the vehicle is cold or warmed up from driving once I get to a steady speed between 25 to (55 or 60) mph the tachometer will drop down between 800 to 1000 rpm and will start jumping up and down a few hundred rmp and the transmission makes a slight reving noise and I have to let off the accelerator a little and the noise goes way but the vehicle slows down and settles out and the noise comes back. I also get this hard jerking coming from the engine and the reving noise buy much louder from the transmission when I try to accelerate but only while I'm already moving above 20 to 25 mph out of 1st and maybe 2nd clutch pack but not at a standstill. It won't shift into a higher gear when it does this and the only ways around this is to let off the accelerator and floor it or to simply press the O/D off button and the rmp will jump up to 1500 to 2000 and it will shift and the vehicle will accelerate.

Please help, I would like to fix this problem over having to trade it in or junk it.