on an auto at the speed of 100KM/H the RPM used to be at 2000.
now after change to manual transmission, the RPM is at 3000 for 100KM/H. Is this normal ?

yes.

congrats on making the switch.

different gearing, of course it will be.

Didn't mention what gear. If that is MT 3rd gear, that sounds right. Can't speak for the AT RPM.

Not many transmission swaps that I have seen, gratz, and we would be interested in more details :)

4spd or 6spd AT? If 4 there is definitely a change.

6speed every 1krpm is roughly 20mph. 20 * 3 = 60...so 62mph = 100km/hr @ around 3krpm

Car specifications:
Greddy Turbo Kit
Microtech LT10s

When using 6AT
No RPM cut
Speed cut at 180kmh (throttle off)
Boost kicks in in 2500rpm
Rpm between the 2000rpm to 3000rpm when at about 100kmh to 120kmh

After swapped to 6MT
RPM cuts at 9000rpm
No speed cut
Rattling noise heard from gearbox/clutch when above 5000rpm
Turbo can be heard spooling, blowoff also heard, however no turbo "pull" felt when driving. (as compared to driving 6AT)
Defi boost guage indicates very low (0.1 to 0.3 bar) boost
when in 6th Gear, travelling at about 106kmh, RPM is about 3300
Sometimes when in the 6th gear, car suddenly loses power and starts to vibrate rather violently when taking foot of the pedal. Funny noises heard from gearbox/clutch area. This is done when RPM is at 3k+ rpm. However when stepping the pedal again, vibration & sound is gone, but car feels very underpowered.
i am still using the same dashboard display (0 to 9000rpm) however have plans to install aftermarket tachometer.

is this just a case of the need to re-tune the car after AT to MT swap? or is the gearbox fucked?

Please help.

when i let off the gas when cruising, my exhaust will emit a few pops. it is "rather violent" though.

where do you live? maybe we can get a local member to help you out. the noise at 5000rpm may be your throw out bearing.

if your car is jerking violently .. it may be coils .. shtt was happening to my car .. scared the crap out of me .. but im guessing you knew that .. im a noob

Car specifications:
Greddy Turbo Kit
Microtech LT10s

When using 6AT
No RPM cut
Speed cut at 180kmh (throttle off)
Boost kicks in in 2500rpm
Rpm between the 2000rpm to 3000rpm when at about 100kmh to 120kmh

After swapped to 6MT
RPM cuts at 9000rpm
No speed cut
Rattling noise heard from gearbox/clutch when above 5000rpm
Turbo can be heard spooling, blowoff also heard, however no turbo "pull" felt when driving. (as compared to driving 6AT)
Defi boost guage indicates very low (0.1 to 0.3 bar) boost
when in 6th Gear, travelling at about 106kmh, RPM is about 3300
Sometimes when in the 6th gear, car suddenly loses power and starts to vibrate rather violently when taking foot of the pedal. Funny noises heard from gearbox/clutch area. This is done when RPM is at 3k+ rpm. However when stepping the pedal again, vibration & sound is gone, but car feels very underpowered.
i am still using the same dashboard display (0 to 9000rpm) however have plans to install aftermarket tachometer.

is this just a case of the need to re-tune the car after AT to MT swap? or is the gearbox fucked?

Please help.

Yes i do have the similar problem! I have a manual 6mt rx8, but engine overheated, so i ordered a new engine, but by mistake, its actually a 6 port 6at engine, and i using carbonetic super single clutch, and totally same experience of what you r mentioned with the jerking sound and feeling. RR please comment.

on an auto at the speed of 100KM/H the RPM used to be at 2000.
now after change to manual transmission, the RPM is at 3000 for 100KM/H. Is this normal ?
Perfectly normal. In fact, should be about 95 or 96km/h at 3000 in 6th gear on a stock gearbox assuming gearbox is from a pre-facelifted model with no change in final drive ratio.

This should help....

http://www.rx8club.com/attachment.php?attachmentid=163402&stc=1&d=1286703557

It's in MPH.