I've had great kindness shown to me recently by AndyT, who has helped me with a really awkward problem with my TS 200 rebuild. Until yesterday, the saw was dismantled into its components, almost completely. We were replacing the rise & fall pivot, so apart from a couple of nuts on one thread, all of the saw was taken apart.
So I know the insides of a TS200 very well indeed, and I very much doubt the TS 250 is very different. I realise access to the trunnion mounts might be, but they're really hard to get at anyway).
There are a few points from this I would mention:
1. if you can't get the blade properly parallel to a mitre slot something is wrong.
2. If you can't get the blade parallel to a mitre slot, using any home made sled will give disappointing results and/or issues like a risk of kickback. It will certainly reduce accuracy.
3. It should be possible to adjust the blade through 90 degrees in either direction. This is so you can set it exactly at 90 degrees. This is also important for accuracy, and it's one of the big reasons for having a TS in the first place. It's also why there is a 90 degree adjustment bolt on one side of the "trunnion" pivot system (IIRC, left side as you look at the front of the saw).
I strongly suggest you take one or both side panels off, so you can see, and find out why neither of these things are possible.
For alignment: There are sliding mountings, as I mentioned earlier. It is possible these are getting stuck on lumps in the table casting (underneath the table). The fix is not difficult but it does take time: you have to dismantle the saw so that you can get to the table and smooth off the pads the mountings slide on. There may be something else, but I can't imagine what. There is, or should be, far more adjustment than needed to get it aligned properly.
For 90 degrees: If it won't go square, something is stopping it from tilting. Find out what that is and fix it.
If you don't do this, you will always be frustrated, as the saw just won't work with the accuracy it is capable of.
E.