as above got a problem with my car, was driving home today from birmingham when i noticed when i put my foot down the car is hesitating

.....
my thoughts are thats its not mechanical, oil pressure is great as is water temps, but when i put my foot down the car hesitates and almost gently rocks forward and backward.
driving the car normally the car is fine i'm running 300bhp, superchips chip 4bar fuel reg. the car has had nothing changed to suggest there could be a problem the plugs were new 2k ago (altho not got to check them yet as its dark).
but as said it only happens when i boot it the car jolts it hesitates then what seems like its missing then when i change gear its fine until i try and boot it again......
my first thought are plugs/coilpacks,leads and secondly it could be the fuel pump as i am unsure if its still the std one or not
But as said the car has never suffered a problem with whats its been running for 6 months never skipped a beat... only 1 problem i had was when i bought the car plug gaps were incorrect...
cheers Ad