Paul still sinned. And he was not bragging about sinning when he wrote to Timothy, 'of whom I am chief.' Nor was he saying that he was chief of sinners in the past but no longer was. 'Am' is a present tense word.
am is present yesterday with Hank Aaron. You need to read all of Paul writings
Rom 8:1 ¶ [There is] therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
Rom 8:2 For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death.
Rom 8:3 For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh:
Rom 8:4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
Rom 8:5 For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit.
Rom 8:6 For to be carnally minded [is] death; but to be spiritually minded [is] life and peace.
Rom 8:8 So then they that are in the flesh cannot please God.
Rom 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
Paul was talking about when he was under the Law and persecuted the church of God and felt that no one had surpassed him in sin that he committed againd Christ, but obtained mercy.
1 Tim 1
8:
But we know that the law is good, if a man use it lawfully;
9: Knowing this, that the law is not made for a righteous man, but for the lawless and disobedient, for the ungodly and for sinners, for unholy and profane, for murderers of fathers and murderers of mothers, for manslayers,
10: For whoremongers, for them that defile themselves with mankind, for menstealers, for liars, for perjured persons, and if there be any other thing that is contrary to sound doctrine;
11: According to the glorious gospel of the blessed God, which was committed to my trust.
12: And I thank Christ Jesus our Lord, who hath enabled me, for that he counted me faithful, putting me into the ministry;
13:
Who was before a blasphemer, and a persecutor, and injurious:
but I obtained mercy, because I did it ignorantly in unbelief.
14: And the grace of our Lord was exceeding abundant with faith and love which is in Christ Jesus.
15: This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners;
of whom I am chief.
16:
Howbeit for this cause I obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting.
13:
Who was before a blasphemer, and a persecutor, and injurious:
but I obtained mercy
16:
Howbeit for this cause I obtained mercy
Was Paul a hypocrit, teaching them not to sin, while he was the greatest of all. I do not believe such stuff and that kind of doctrine will send a many of a man to hell.
Greek for "am" eimi
Strong's
1510
eimi
eimi
i-mee'
the first person singular present indicative; a prolonged form of a primary and defective verb; I exist (used only when emphatic):--
am, have been, X it is I,
was
