C5 transmission help.
 

The C5 transmission in my hubby's '83 F100 truck will not shift into reverse anymore. After about a year of owning the truck, it started to shift pretty hard when putting it into reverse. A few months later we lost reverse all together. Everything else works fine on the transmission. It shifts very smoothly into 1 -3. He has replaced the reverse servo, drained and replaced the fluid (no metal pieces were seen in fluid) and thats about it (so far). If anyone can help figure out whats wrong, I would really, really, REALLY appreciate it. Thanks so much!