I have almost no reverse on my truck which I believe is a 47re transmission? It will intermittently move on flat ground with a lot of shuddering akin to riding the clutch in a manual, but most of the time will just sit and rev. The truck is smooth as glass and shifts fine in all forward gears.

-The fluid is full plus a quart of Lucas which did not seem to make a difference after a 15 minute highway drive to mix it in.
-I can move the truck forward locked in first. I've been told several times that this rules out the reverse band since I'll also lose first with a bad band, what say all of you?

That brings me to the shift linkage as a possible culprit. There is a lot of play in the PRNDL lever and the marks don't quite line up on the dash but not severely off. When I select reverse there is a noticeable thunk like something engaged, and I can see from the way the tach moves that there's a little more friction than N. So it feels like it did find reverse but maybe not all the way engaged? I inspected the shift linkage from the transmission back to where the cable heads up to the dash. There are no obvious missing parts but there is a lot of play in all the components under the truck, I can rattle the linkage assembly with my hands. Can anyone help with the procedure for checking the linkage adjustment or comment on whether the linkage assembly may be worn out? I've been surprised at how little information I can Google on this one.

I'll take any other suggestions you have for possible causes, the shift linkage is next on most of the troubleshooting lists I've found and I figured with how sloppy it is in the cab maybe something is there.