i have patrol SWB with 4.5L "carburetor", the car has cut off or rpm lock at 3600 !!! so i have to shift the gear to next one which means lose momentum, or even get confuse during a side crest which could be dangerous

i went for many shops in Mussafah, they start guessing or they only fixing patrol injection engine only!! like sana shop.
when i got the car before 2 weeks and as an maintenance i changed the gas pump & filter, sparks and cables, coil
does any one face same problem or know where i can find some good garage in abu dhabi fixing nissan carburetor??
Thanks in Advance