Having tried many fluids the best for a getting a "touchy" transmission to shift well is Redline synthetic. Its available in two grades: "MTL" which is 70W80 from memory and 90 weight. Either one would work in an 833 - I'd suggest the MTL for easiest shifting with adequate protection of bearings/gears. Summit and others sell it.

I believe the ATF and syncromesh options are too light for an 833 (I know, controversial topic). That said if it won't shift smoothly on syncromesh you might well have problems with the hard parts as posted above.