help hesitation on my gtr

[donkey]

hey i have a r33 gtr v spec, it is running an apexi computer with hand controller, has done 160ks but well looked after, my problem is driving at about 120 kph, in 5th gear has a slight hesitation every half hour or so, also sometimes on full boost in 2nd gear (1 bar) at verying rpm will basically cut out, any help would be great.....robbie