2010 transmission slip

[iajet]

I have a 2010 Explorer 4WD with about 30K miles and in first gear I intermittently (could happen once or numerous times a day, of course it doesn't happen at the dealership) get a slip/thud at slow speeds. It happens at slow speeds (first gear) slowly accelerating from a stop or sometimes turning a corner on an incline. The other night I noticed the stability annunciator (can't remember the name for it) illuminate as the slip/thud happened. It doesn't seem to matter whether the engine/trans is hot or cold.

About a week ago I had the following work done hoping to fix the problem.
-solenoid assembly
-new fluid
-piston-low reverse servo
-automatic trans main control valve
-automatic trans solenoid valve

I took it back to the dealer today.

I am pretty handy but have no experience with transmissions so the parts above don't mean anything to me.

Any thoughts or ideas....?

I would like to be able to suggest a few of your ideas when I speak with the dealer tomorrow.

Thanks so much.