Welcome! My name is XXXXX XXXXX X will do my best to assist you with this problem.
will it run rough just at idle or when driving at speed ?
when at speed it runs and accelerates just fine but you can feel a vibration when when you decelerate.
will it do this at idle or in park revving it up a bit ?
it will at idle and in park revving it up.
ok if it is doing this in park when you rev it up its the engine or possibly the torque convertor
what you can do is remove the torque convertor bolts so the convertor is disconnected from the flex plate if it still does this its the engine running poor causing this or the engine is out of balance from the flex plate or possibly the front crank shaft harmonic balancer
Just fyi. I just discovered a leaky injector on the front passenger cylinder ,