I know this problem has been discussed recently on this list, and as I
remember it has to do with one of the temp sensors.

I just installed new head gaskets. So far no leaks, started right up,
system bled and the loud clatter from the lifters has gone away. But I
can't drive the car (very far) because through it runs sweet on
startup, it starts emitting dark exhuast, runs rough, and soon the RPMs
slow to a stall. I can pull the throttle to keep it running as long as
I want, but if I don't keep the revs above 2000 or so it chugs to a
stop.

Turning the key "resets" it to run fine for a minute or two, then the
symptoms return. It doesn't matter where the engine is in the temp
range, it seems time-related.

Any help will be appreciated, of course.

Jim