I'm going to suggest tailshaft balance. Have gearbox/diff fluid levels been checked?
The BA diffs apparently also have backlash issues but I know little about diff internals
Proud TQE Operator and President of SEFAG - the Society for the Elimination of Ford Automatic Gearboxes
Pacemaker headers + 2.5" exhaust
EF Fairmont interior
Lowered King springs
5 speed manual
Newest mod: EF Ghia wiring loom and dash