When I accelerate over 50mph the car jerks repeatedly for about 15-20 seconds and then accelerates with no problem. 3 months ago I had all plugs replaced, an oil change and a fuel filter change. This is all I've had done since I've started driving this car. What could this be?

Welcome to AF. Possible ignition misfire, possible tcc slippage, someone has to drive this to diagnose the condition.