If you still have 1st gear but no engine braking, then the link between the low reverse band and the servo arm fell out (I have had this happen before) The link will be in the pan probably, you can fix this without removing the trans, but you might have to remove the valve body depending on where the link ended up. Drop the pan and take a look. It usually falls out because the low reverse band is way out of adjustment. If you have no 1st gear at all, then the low roller went out or something else. TAC will chime in....