What should I do to stop jerking when the shift gear changes?

I've recently had a tune up, oil changed and even change my transmission to see if the jerking would stop but honestly speaking even after doing the full complete tune-up(distributor cap spark plugs, motor, pcv valve,filters,etc...) it runs a little smoother but every time the car is at 15mph and 30mph it slightly jerks before acceleration continues...I've asked a mechanic and told me its an old car and will do that.....should I do a transmission flush and add new transmission? at the same time I also heard fuel injection cleaners and system flush cleaners can actually harm than do more good to the car.. Those system flushes were suggested when I did my oil change.... my car is a used 1996 honda accord lx with a mileage129,00 been driving it for one year and 5 months now...please help...I just want to keep my car n gr8 running condition