1995 Lexus ls400

Goodness Hashir, Im having the same problem with my 1995 lexus ls 400(same engine, same trans, near miles). I recently had the$$ transmition $$replaced, not even two weeks later, this trouble starts. The funny thing is it dont happen all the time, one day its fine the next this problem arise, my mechanic is great, years of exp but he cant even trouble shoot this thing. He assumed many things like some type of swith the goes in the dashboard, replaced that, no result. He assumed replacing the whole steering wheel, no results. My mechanic is usually great but I refuse to keep wasting money for parts. Have you found out anything? Somebody?