Bump bump under load now reverse gone

[backroads]

My 98 xlt 4.0 sohc auto went down today.For awhile it would go bump bump under load (you could feel the bumps) and this morning I put it into reverse it went bonk! and reverse is gone.
Any information I can get to arm myself with to talk to my tranny shop guy would be helpful.I'm not going to do this myself, and the tranny shop is owned by a friend of mine but any info about what went wrong would be very helpful.
Thanks
Mitch

 

[Glacier991]

In the 5R55E a lack of reverse can be caused by a number of things. First off the Digital transmission range sensor can be bad or out of adjustment. Fluid levels can be off. The filter can be plugged, the valve bodycan be in need of attention, especially the valves in bores 203, 204 and or 205 could be stuck. The pump could have become damaged, and the biggie is the reverse clutch... it could have taken a trip south on you.

Likely a rebuild is in your future I fear.