240sx guys come!! help meee!

okay well i recently did a tune up on my car because of the bogging (spark plugs, wires, dizzy cap, rotor, etc) but i ran into one wierd problem today... as my car runs good first and 2nd gear.. when i shift to 3rd it suddenly runs like its on 3 cylinders or a spark plug came loose? but all of them are tightened and such.. and after it hits 3rd gear and bogs the rest of the gears do it 2.. (1,2,3,4,5).....


any ideas...