2 days ago, while driving and on climbing a little hill, I realized my truck was not moving, When I tried putting the car on park with the engine running, it made a loud rattling noise. I put the truck on drive and pressed on the accelerator and the car just stalled. Called tow truck, and towed it to my house. Next day when I started the car and put it on drive, to my surprise, the car, once more moved.
At this point every indication points to the transmission, my question is why did it suddenly stop, the night before and a can now move. I have it parked in my garage, scared stiff to drive it and want some opinions before taking it to the dealer, because this people can always come up with some exorbitant charges

It helps if you state your year and mileage etc. Really not much to go on with out it.

Do not drive it at all. I had a similar instance that began last week (very brief stalling, slight gear hesitation . . . etc.) It would occur off and on every 2 days until last night I suffered a total transmission failure. I own a 2001 2WD Lincoln Navigator with 65,000 miles and I am terribly disappointed. Has a recall been issued for the transmissions ? It may be a valve situation that can be readily corrected. However, a dealer can't take down your transmission and run the risk of you returning with the same problem after fixing the valves. Based on the amount of work to get to the valves, you face a steep mechanic charge for parts and labor as you consider a new tranny from the dealer or a used one.