It feels like less power in initial pickup i.e 1st gear and even in 2nd, 3rd gear. Replaced air filter. Even carburettor cleaned. Oil changed recently.
It's hard to say, as there isn't much info to go on. A few things to check:
1) Check the spark plugs to ensure you're getting a good spark. Replacing them could help.
2) Make sure you're using fresh fuel. If you have a fuel filter, try replacing it with a new one. Has the bike been sitting unused for any length of time? Bad fuel or fuel that has been sitting can clog up the small passages in your carburetors causing fueling issues.
3) Check the air filter isn't overly dirty, and replacing it or cleaning it if possible.
4) If none of the above issues fix the problem, I'd start checking compression on each cylinder and make sure it's within the spec listed in the service manual.