ok, problem finally found and solved. i took the deck off and lifted the front end, traced the connecting rod from the foot pedal to the transmission. i did not see anything wrong.
as i was using a neighbor's lift, i asked him to take a look and he found it - a stick about half an inch thick and about 2 inches long lodged vertically behind the assembly of the
control rod at the transmission. it allowed the lever at the transmission to move forward but blocked it from moving back. it took about 10 minutes to get the stick out of there as
it was in just perfectly - i don't think i could recreate this episode in a million years!
mower works fine now. thanks to all who replied.