hi - ok - i will bite

A few points...

1. you name structures confidently and have the name "doctor" - waht is your background? It doesn't really matter to me but it might put other people off...
2. You believe everything is "tight" but it is likely to be overactive
3. The problem alternates which indicates to me that it is likely to be a myofascial or neural (motor control) type of problem rather than a fixed joint. I suppose it could be a joint which has too much laxity from exceiive manips...
4. You state you can't transfer load efficiently and have trouble controlling rotation - again, see point 3 above
5. You believe your RWikipedia reference-linkSIJ keeps unlocking - why is that - what test and how is it done that convinces you of this?
6. You can get it to lock doing exercises - see point 3 above!
7. Summary - you are a motor control and myofascial problem - multi joint

Lots of retraining is needed on normal movement, posture and letting the resting tension of some muscles calm down.

It is way too hard to solve over the internet unless someone over there knows what they are doing.

Also, the above is my best guess based on the information you have given me.

Cheers!