My mazda 323 gear 3 is slipping even though the mechanic cleaned the censor and addednew tranmission oil and wynn's treatment..wat is my next step

Find another mechanic Crystal. This transmission should have been rebuilt from the beginning.

Mr. Barnett, is it carb. or injection. If it is carb possible you do have a dirt inside the car where you surely need a mechanic to inspect and clean. If your vehicle is injection then are the following :1. either the throttle body is dirty on throttle and needs cleaning, 2. probably the air flow meter is faulty or dirty, 3. the fuel pressure on acceleration is not sufficient,4. fuel filter is nearly logged. Ask for a mechanic to help you is better instead you try to if you do not know many things about mechanics.

I was involved it testing 3 types of additives for oil a long time ago and the only additive that worked and did what was claimed was Wynns. STP along with Bardill failed the test and proved to be not better than good quality oil. I use Wynns in everything ( cars ,rotaries, lawn mowers wiper snippers diffs gear boxes ,wheel bearings "U" joints --everywhere there is friction) I have over 400.000 klm's from my original RX7 motor still going strong , over 250.000 klm's from a Mazda bravo motor , 8 years from a lawn mower. . Personally I would not even consider STP or any other additive for that matter for friction proofing.

check the oil

Check the engines compression. This has been known to happen on real tierd engines that have poor compression, with it comes lack of power from the combustion cycles. If the rpm is raising quickly, and speed isn't, your clutch could be slipping.

check the condition of the oil and see whether you have filter in the gear box. Do a flush after renew the oil and filter and clean also the oil cooler of the gear box.On renewing the filter and oil also add a WYNN'S Auto transmission treatment additive.

Check oil level in transmission may need to change oil .I have done this before bad is bad oil you will be surprised at what clean oil will do.

Check the overheat sensor switch (usually located in the cylinder head) is not faulty.
Check sensor connections are firm - ensure no possibility of short to ground.

Automatic and standard transmission needs fluid change every 24 months. On automatic transmissions, the gasket needs to be changed as well as the filter. On standard transmission there is a drain plug that can be loosened up, and refilled through the refill hole. Standard transmission use gear oil, while automatic transmission uses automatic transmission fluid.

through the speedometer gear behind the motor on top of the tranny there's a 10mm bolt holding it in the just pull straight up at the base and then ad fluid there.