I have a x5, 2003 model, it's not rev above 3000 rmp at most of the time. and it's just accerlarate slowly up to 60 km/h and that's the max speed. the promble will remove when idle the car for 10 minutes before, but after I parked the car for 2 weeks, the promblem contantly occurs, I can asure there is no promble with fuel supply. Is anyone can help me out of this?

no country told , matters! for sure no USA. KM speeds tell that. GUESS Australia????
down under IRON./? or the exported Austrilia to Africa.???

won't rev out (means RPM limited,means low power from engine. so means engine power is lost.
and NOT:
not transmission slip. (none told A/T or stick?)
good post, lots of causes for any kind of engine power loss
I will not pretend to guess it but in terms of physics yes.
engine has mech problem , cam belt slipping then changing back.
engine low power.
does 4LT mean 5liter engine, or 4L +LT MODEL CAR
The BA sub model falcon? IDK
wiki says

• 4.0 L Barra 182 I6 (petrol)
• 4.0 L Barra 240T I6 T (petrol)
• 4.0 L Barra E-Gas I6 (LPG)

seems there are 3 engines used, day1 sold,
gas Petrol
turbo petrol (gasoline)
and LPG (propane) gas.

deep wiki' me.
182 is 6 cylinder DOHC cam engine with pesky VVT valve timing
chain drive cam +VVT
VVT can stick so there is my first physics IDEA on engine problems.
or stick head valve.

the classic list, (means what is tested in order.) using tools.
1: good engine, means all tests pass,and VVT'
2:good spark ever do a tune up in 20 long years,spark + filters.
3: bad fuel, or bad fueling rates. , fuel pump on lasts legs. sure.
4: egr struck open ,even random they do.
5:;random bad wiring to all that.

that is my best, 12,000 miles away and blind, cant see car engine or transmission there.

1st have the system scanned for fault codes, based on the codes perform diagnostics with the factory service manuals at hand.

If you want to know about this model I suggest you visit the Wikipedia page below.

https://en.wikipedia.org/wiki/Fiat_128

their are 16 models for the anglia in 1966 using the higher hp /manual set up --Anglia 105E-123E Saloon model for Europe North America , 2-door sedan with manual 4-speed and 1198 cm3 / 35 40kW (47 54 hp / 48 54 PS);--------- Acceleration:0-30 km/h (s):2.20-40 km/h (s):3.50-50 km/h (s):4.60-60 km/h (s):6.60-70 km/h (s):8.50-80 km/h (s):10.90-90 km/h (s):140-100 km/h (s):18.50-110 km/h (s)24.40-120 km/h (s):34.7----------Drag times:0- 1/4mile (s):20.4speed at 1/4mile:103 km/h / 64 mph0- 1km (s):38.9------- Top speed: 132 km/h / 82 mph http://www.automobile-catalog.com/auta_perf1.php

When you rev the engine and does not go over 3000 rpm is this in neutral or when driving in gear? Some vehicles have a rev limiter to not allow rpm over certain point when in neutral gear but is typically not limited when driving vehicle. This sounds like a very low rev limit but not abnormal if you can get engine to rev higher when driving. You call a drifter so truck must be non US market. Is this engine a 2.5 liter diesel 4 cylinder motor. Might just be your top rev and speed if this is the case.

TPS (Throttle posision sensor) would be my guess

It almost sounds as if the rev limiter is kicking in.

Stock Tire - 245/65R17
Revs per Mile:704.3
Overall Diameter: 29.53 in 750.06 mm
Actual Speed: 60 mph 100 km/h

Tire 1 - 275/60R17
Revs per Mile:693.5
Overall Diameter: 29.99 in 761.74 mm
Speedometer1: 59.0 mph 98.4 km/h
Speedometer Difference: 1.557% too slow
Diameter Difference: 1.54%

Will fit with the stock rims.

The owner's manual calls for changing oil and filter every 7500 miles in normal service, or if driving in dusty conditions, offroad, or lots of low speed and idling (a taxi or maybe an unlucky commuter), go to the extreme service intervals of 5000 miles. Changing oil every 3000 miles is definitely NOT required.

Was the vehicle a previously rental vehicle? because if it was there is probably a speed govenor on it or a rpm govenor on it most likely a speed govenor if a previous rental vehicle