Just an update to this thread - it's been 18 months and I finally got the issues with my fuel filter resolved. Took the Chieftain for a ride after draining a couple of quarts out the transmission behaves the same. Single upshift, and no shift to 4th. I think this trans has to come out.
I also finally traced the coolant leak I though was coming from the intake manifold gasket. The expansion plug (freeze plug) in the rear of the left head has rusted through. Looks like the only way to deal with that is to pull the head. I'll start a separate thread on that.
Yay for old Pontiacs . . .