Engine vibration through gas pedal

Cadillac cts 2003 having a performance issue. Not sure exactly when happened before or after tranny line blew out of radiator. Only way to describe it is. Car would run as smooth as silk and got up and went like nothing. But about 96% of the time it drives like its being held back a little. I can feel difference almost like engine vibration through gas pedal too and slight power loss in performance. Sometimes it drives a few gears like nothing is wrong and performs at 100% and its so smooth and performs great. I just had spark plugs done and a coil pack replaced. Also a Mobil express shop added 2 quarts of tranny fluid after I replaced radiator. Any help on that issue would be fantastic. I want the old way it drove. Ive only owned car for about 2000 miles. Dealership suggested I do a fuel injector service, do I really need that? 117000 miles on this car. Prior to the performance issue Also I noticed that around 40 mph when car shifts here its a little rough, any insight?