Dead spot in throttle

Hi I have a 1997 Mercury Cougar 4.6 with
116000 miles. It has had this problem lately
where there is a dead spot at about 1/4
throttle but the rest of it is fine. Even if your
in park and you slowly rev it up it will hit the
spot and act like you let off the throttle but
then it kicks back in and is fine.I scanned it
and it gave me o2 sensor on both banks
and running lean codes. I changed the TPS
and two o2 sensors right below the
manifolds, nothing happened. Then I
decided to unplug the o2 sensors and
disconnected the battery and hooked it
back up after a few minutes. That got rid of
it when you slowly increase throttle but if
you Crack the throttle it falls on its face. Any
help would be appreciated I'm just getting
sick of it. Thank you