this morning when i went to back out of my driveway my transmission made a loud clunk-thud noise and wouldnt move unless i pressed the gas. sounded kinda like the gears wouldn't lock, then they did. idk. it only did it in reverse.

i have a 4R70W auto tranny in a 2000 f150 5.4
keep in mind it was 28degrees this morning. its never happened to me untill now.

i assume reverse still works. ill try after school today.
anyone had this happen to you? maybe i need to change transmission fluid?? this tranny has about 25K miles on it and is used primarily in city driving. no towing. has no shift kit in it or anything. its completely stock.

any thoughts???