I think you need to be a little more realistic about how soon someone is going to see and respond to your post. 6 minutes ?? ... it could be days
The condition of your pan should reflect how you drive. If you're a heavy foot and love to play with the power and show others you can beat them I'd say it's normal. If you drive it more like a daily driver and don't really plant your foot to the floor very often then I'd say that's a lot of material to be sitting on the bottom of the pan and on the magnet for 30K.
It would also depend on if you had a massive failure before the rebuild and how well everything was cleaned and or flushed before re-assembly.
IMHO It might be a sign the transmission isn't applying enough pressure and you're slipping excessively between shifts.
I've seen trans with 100K look a lot cleaner than that. Their fluid looked and smelled like crap but there wasn't that level of material in it
BUT, to qualify that, those were un-blown daily drivers that likely never raced anyone anywhere.
You say it was rebuilt, was the cooler in the radiator (or external) flushed before re-installation and what was the reason it was rebuilt ?? Massive failure, slipping, lost a gear, just wanted to "J" mod it or add some HD components ???
Was it a DIY rebuild, a "friend" or a transmission shop??
How does this transmission feel when it shifts? Does it feel it's a firm shift or does it feel like it's slipping from one gear to the next?
If it was me and I was sure the stuff I'm looking at wasn't left over from before it was rebuilt I'd spend some time to find out a way to up the pressure on the shifts so they were more likely to be uncomfortably firm and "bang" from gear to gear. More so if you're doing any street racing or just beating on it.
If I remember right I think the "J" mod had directions for different power levels and it had to do with having firmer shifts as in higher pressures for the higher horsepower engines.