i really don't know how to describe this, but my Z is acting a little funny. when i first start to accelerate in first it sounds as the idle drops too low while i am bringing out the clutch, but the idle is not dropping. it just sounds wierd (sorry, i cannot really explain it). then, if i goto 6th gear around 50-60mph the car seems to shake and lug a bit under the load. the same in 5th gear. this happens around 1500-1800rpms. it kinda feels like a plug wire, but they are all good and the plugs seem to look good with a nice gap (not sure how to read plugs after spraying N2O across them, though. i have probably 8 bottles on these plugs). anybody have any ideas on what this could be? the car is fine and sdoes not have any problem under hard acceleration or in any other gears. just the low idle sound in 1st and the lugging at 1500-1800 in 5th and 6th.

any ideas?