2003 Jaguar X-Type Bucking, when going up hill and taking c

My car has been acting strange lately. I noticed when I go up hill or taking corners, it seems to get sluggish and almost lose its power. There is also bucking of the car when this happens. The car was bucking when I was on the highway also goind above 55 miles and hour, I could still fell the bucking although slighlty. I replaced the spark plugs, fuel filter and air filter thinkg this would help and the car was due for that to be done anyway. I noticed a slight difference as its not doing it on the highway anymore but still doing the same thing going up hill and when taking an off ramp or taking a corner. I also replaced an oxygen sensor not too long ago also as the service enging light came on and thats what the problem was for that isssue. The delaer did tell me, there is an air flow sensor and also another oxygen sensor in my particular car. He said those may need to be replaced but dont do anyhting now until the service engine light comes on again. The service engine light has not come on but I know I have a problem somewhere. Some people have suggested I change the fuel pump. Do you have any idea what this might be. Otherwise the car runs fine, starts up right away.