On ocation my 91 Ranger XLT 4.0 auto starts cutting out at 55-56mph. At times I can hear a scratchy sound under my hood while driving next to something that can bounce sound while driving. I hear it only when cut out will happen.
Connect a vacuum gauge to the intake and mount it on the windshield in plain view and see if anything is indicated on it at 55-56mph.
possibly electrical wires shorting out. bounce sound maybe something separate. can you record the sounds and post it here?
make sure your battery is held down properly. if its bouncing around it could be both your problems. bouncing noise and battery post shorting out. just a thought.
My guess, some sort of ignition system problem. I’d start by replacing the spark plugs, distributor cap, and rotor. While you have the dist cap off, see if you can get much play by pushing on the distributor shaft from side to side. There should be very little play. If there is you’ll need a new distributor. Of course this assumes your engine uses a distributor. I think a 91 probably does.