It sounds to me like your transmission has worn out the B3 clutch pack. I've seen this several times and it only causes the loss of reverse. To get to the clutch pack you'll have to remove the trans. and it's front cover. The outer ring of clutch plates is the culprit. You could probably just replace the B3 parts but pay attention to how hard the rubber seals have become. This is usually what causes trans. failures.