shake in 5th

ok starting last week i felt a shake between 100-125, now its like a rumble, but its only in 5th. if i put in in forth it goes away. any thoughts.

Second lol

now every time i slow down the car feels like its going to stall, or when accelerating the car has a hesitation or shutter feeling. i don’t now these cars very well so any help would be great

What motor?

ka