I should have added cautions to setting the tv (throttle valve) cable.
but check the tv cable before doing anything else.
If it set to loose the transmission could fail.
to tight and shift points will be high, and when coming to a stop trans will not shift out of 3rd or 4th soon enough and since these gears are driven directly off the crank the engine will fight the brakes. Feels like you are being pushed.
Quick no tools trial by error procedure.
When the throttle is closed the slack on the cable should just be taken up.
There is usually a clip of some sort on the throttle body side to let the cable be adjusted.
Adjust back and forth to best performance, but never allow slack in the cable.
My preferred method is to use a mechanical oil pressure gauge attached to the tv port on the driverside of the transmission. Does not have to be a high quality guage. With throttle closed the tv pressure should be 0 with tension still on the cable. As soon as the cable is pulled, the tv pressure should move off zero. You can push the end cable stop crimp to the side to test this, it will act as a lever and pull the cable out ever so slightly.
Ford has a tool to pull the cable out set distance and then the pressure is set at 32 psi, but I find the above method a little better and ford even states the no tension and pressure at 0-5.
If shudder still persists change the transfluid and some dr tranny rx instant shudder fix.
If still shudders I would bet the direct clutch is failing.