hesitation on cold start popping in plenum

[mlozzi200478]

i have an 89 300ce, replaced both fuel pumps with high flow fuel systems pumps,replaced the ovp,replaced fuel filter,had air fuel ratio calibrated,now i just need to replace the o2 sensor,car has to warm up for about 10 mins,or it will hesitate taking off popping in plenum,bucking then finally taking off and driving normal,but it still lacks full power,and when it down shifts it stays reving until i lift accelorator,does an o2 sensor cause this much issues with fuel,i was told from my mechanic all this would solve the issue,so i wonder if anyone thinks just the o2 sensor will solve this,thanks poeple.