Not once does Paul indicate a difference between sins. It's sin - period.
There is nothing to forgive. Either all our sins were forgiven at conversion, or none of them were. Asking God to forgive us for our sins after being born again is ridiculous. He has already forgiven them. Why are you asking for forgiveness for what has been washed away by the blood?
Well, I see evidences that Paul did preach the necessity for repentance:
2 Cor 7:10
10 For godly sorrow worketh repentance to salvation not to be repented of: but the sorrow of the world worketh death.
KJV
2 Tim 2:25-26
25 In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth;
26 And that they may recover themselves out of the snare of the devil, who are taken captive by him at his will.
KJV
And the passage below, in I Peter, shows that if believers fail to be diligent in keeping sin out of their lives - the result is losing their salvation:
2 Peter 1:5-9
5 And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
6 And to knowledge temperance; and to temperance patience; and to patience godliness;
7 And to godliness brotherly kindness; and to brotherly kindness charity.
8 For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.
9 But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.
KJV
And the passage below, shows that the need for repentance is not just a one-time thing - no longer needed. No, it is needed:
Matt 5:21-24
21 Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:
22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
23 Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee;
24 Leave there thy gift before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.
KJV
Also, Jesus taught the need to pray for forgiveness, in the model prayer He gave. Being a model prayer, it represents things we should pray for daily in daily life:
Matt 6:9-15
9 After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name.
10 Thy kingdom come. Thy will be done in earth, as it is in heaven.
11 Give us this day our daily bread.
12 And forgive us our debts, as we forgive our debtors.
13 And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen.
14 For if ye forgive men their trespasses, your heavenly Father will also forgive you:
15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
KJV