A fluid and filter change addresses the lubrication and filtration aspects, but not the mechanical wear and tear inside the transmission. While a clean fluid might improve things marginally *temporarily*, it's not a cure for significant internal damage. The slipping is a symptom of a deeper problem.
Think of it like this: if your car's engine was making a loud knocking sound and burning oil, changing the oil would make the engine cleaner, but it wouldn't fix the knocking caused by worn bearings or piston damage. The transmission is similar.
In short: While a fluid and filter change is a cheap and relatively easy first step to try, don't expect it to fix a transmission that slips in all gears at higher RPMs. A professional transmission inspection or rebuild is far more likely to be necessary. Continuing to drive the car in its current state will likely cause further and more expensive damage.
