Try this, while driving at about 20 mph, downshift to manual low (pull shifter into lowest gear) if it just freewheels (dont slow down) the reverse clutches are dective! Trans. needs to come out. This way YOU will know what is up! Sounds crazy i know but that is how it's tested. Post results for more info.
Does this mean that the reverse actuator needs to be replaced or at least the rod inside of it . I lost reverse in my 93 suburban and someone told me to take out the reverse actuator and weld 2 mm to the tip. And I noticed that they sell a new end to put on the shaft instead of welding it only $6 so I purchased and will try once I have the parts.because my tranny as no issues going forward and never even slipped in reverse it worked then it didn't. I'm just trying to get ideas instead of just junking thee tranny