'89 GA sluggish accel

'89 GA - 2.5 TBI engine U ---- Runs and accelerates fine first thing in the day. After warmup, sluggish acceleration. Have replaced plugs/wires/coils. What should I look at next ? (All sensors are original - never replaced.) No SES light or codes. Currently cleaning throttle body and IAC, throttle body gasket appears stained.

Thanks,
Mac