update: found a few things. first, the EVAP vacuum line near the fuel filter was broken, so i fixed that. i think it was unrelated to other issues, but was sometimes throwing an EVAP DTC.

second, i removed the fuel pump and found that the supply line was slipping off the pump discharge, above the check valve, hence the immediate drop in pressure and low fuel pressure overall. I was getting 28-30 psi at the rail. Under heavy acceleration, car would lose power, almost like ECU was capping throttle due to lack of fuel (my theory). Fuel econoomy was 15-19 in town and only 21-22 on highway, and long term trim was +25% on my generic scanner, which i guess is lean.

After re-installing the fuel pump, fuel pressure tested at 43 psi (300 kPa) at the test port near the fuel filter. Car starts within a few seconds. Long term trim is at zero (+/-) and mpg back to 20 in town and 25-28 on highway. Power under load is way better.

thanks for help Klaus and others.