Torque Converter clutch failures

[Tom]

When my 200k mile 4L60E went out a couple years ago I went ahead and put a rebuilt torque converter in it as well. The lockup clutch in that lasted maybe 10k miles and then failed. It was a big name rebuild company that I shouldn't have gone with to begin with, so I replaced it with a TC from the local company my trans rebuilder recommended. I also replaced the TCC solenoid with an OEM part for good measure.
Well, 20k later and I'm getting the same failure. It starts as the truck shuddering after going down the freeway 15min or so and encountering a slight uphill. Eventually it unlocks, stays that way for a few min, then locks back up like nothing happened. I know it'll get worse as time goes on until it won't lock up at all anymore.
Besides confirming the trans is still getting a lockup signal when this happens, anything else I can check that might be causing this that's not a bad converter itself? My 98 GMC btw....