"I use a strap wrench to hold the balancer while torquing the crank bolt."
That's unfortunately a really bad thing to do. The harmonic balancer has a thin elastomeric ring separating the hub and the dynamic mass/pulley. You've likely damaged it. New OEM ones usually cost $300 or so, retail ...
Fixed Up a white 2001 P-code SE Sedan
including rebuilding the SPI (see my threads)