If you have added lots of oil but some of your valves are still slow/sticky, try cleaning them as shown in this video.
Notes: Only out and clean one valve at a time (not all 3 at once like this person does) in order to avoid accidentally mixing up which valve goes in which spot when putting them back in again.
You can use a chopstick and a cut-up piece of an old T-shirt instead of the flute rod and cheesecloth. Just make sure that the stick is fully wrapped so that you can’t accidentally scratch the metal inside the trumpet.
When adding oil again before putting the valve back in, use 5 or 6 drops and twist the valve back and forth a few times to spread the oil around evenly inside the casing before lining it up straight and screwing it back in place.