Question, 240sx throttle response

[swap240]

hi all, i own a '93 240sx 2dr. HB manual 114 k on the motor and when i go to get on the throttle it hesitates, sometimes for a few seconds. the best i can describe is that its almost like a bogin out sound, hesitant for a few secs than its fine untill i go to get on the gas again or shift. no matter the rpm. Also at around 3.5 - 4grand after this it has absolutly no power gain. Its basicly stock except for the K&N air filter/ oil filter/ fuel filter/ not sure about fuel pump/ large after market exaust system 3 1/2 in maybe bigger/ stock headers. Could it be my transmission? My clutch? im clueless, i was beatin by a chevey cavilier, on the highway.. and i do know how to shift thats not the problem although advice or some numbers for when to shift as far as rpm would be of some use thanks alot guyz. any help will be of good use.

[D-Bo]

i would have suggested checking out your fuel delivery system but if its all new then it might not be a problem.. just check if you're getting good mileage and that will tell you if you have a possible leak (if you can't find one)..
take out your mafs and clean it too..

as for shifting rpm, there's an optimum shifting range and you should be able to find out what it is on your car just by feel.. do a 3rd gear pull and note where you stop gaining speed significantly. it'll be just before that..