tritron

I run diagnostics on my car 95 sc300 and I got code 63 so it means bad solenoid. I search the forum and I get is impression that is easy to replace solenoids, one of the posts stated that it could be wiring issue. How I go about making sure it is solenoid that is bad. My car when I drive after ecu gets reseted just fine and transmitionshifts fine then it gets worst. The o/d light is of my dash, according to manual means that there is less than 8 errors given to ecu.