A couple quick ways to troubleshoot your processing
1) check your camera - run a roll of slide film through and have it processed at a decent lab. Exposure problems that are equipment related will show up.
2) Start from square 1
Mixed at factory recomendations with distilled water at proper temperatures.
Process your film at rated speed at the manufactures recommended time.
3) if your problems are actual damage to the film then you need to determine whether it is happening in camera or during processing.
Inspect the slides you shot earlier for damage.. If no damage inspect your reels for damage/burrs/etc Often damage to film during processing occurs while loading onto the reels.. best thing is to practice loading a blank film in the light until you can do it smoothly.
Lots of people here have developed their own preferrred mixes, temperatures, film speeds, etc.. This is fine once you have established your own baseline.
The best place to start is at the stock mixes. Old chemicals/old film/etc are not good to play with if you are having problems..
I hope this helps.