While driving home today, I heard a faint grinding noise. At the next stoplight, I pulled to a stop, and when the light changed, I pressed the gas to leave, and the truck felt like it was stuck in high gear. It took until about 3000rpm which it reached very slowly, before it would shift into another gear. I attempted to floor it to see if it would downshift, but it wouldn't. Also, the O/D light is blinking. I know that means it has received an error code, but does anyone have any idea what the problem could be?

2000 F150 XLT extended cab 5.4 automatic

PLEASE HELP !!!!!

 

I don't, but I'll bet the error code would help a lot.