Here goes the rabbit hole...found another thing that might do it:
- Anti-jerk "_AJ_" retards ignition during rapid throttle opening to smooth out torque (can be removed by increasing c_tco_min_aj to 142.5C).
I was surprised how easy it was to upload the new maps to the car using MS4X. Was expecting some errors and troubleshooting but it worked right away.
For the record, I did go ahead and replace the fuel pump with a new Carter unit. It seems "somewhat better" (although I've learned that when a problem isn't totally fixed, any improvement is usually a placebo).