The Scriptures never indicate that a born-again believer has a sinful nature. We certainly are capable of sinning, but it's not because we have a sinful nature any longer.
We have *one* nature which, before being born again, is entirely bad (sinful and anti-God). This nature equates with our spirit.
When we are born again, this nature is made new (2 Cor. 5:17). We still have one nature, but now in our new nature we love Christ and hate sin.
We still have some old habits, old "programs", old thinking and behavior patterns, physical desires and cravings, etc., and sin itself, which resides in our members. But this is not our new nature. Those old thinking and behavior patterns lust or "set their desires" against our new nature, our spirit (Gal. 5:17). It's what the Bible calls the "flesh" (Greek sarx).
Paul makes it clear in Romans 7 that sin still dwells in us, in our flesh, but that it is not us. He says, "I realize it's no longer I who do it, but sin which is in me."
This is important, because if we think that our new nature is a sinful nature, we will think it's "natural" for us to sin. Actually, the Bible teaches the opposite, that it is "UN-natural" for us to sin now (that is, it goes against our new nature).
We died to sin on the cross in Christ, and we are (in our new nature) now dead to sin and alive to God (Rom. 6:11).
Unfortunately, some Bible translations such as the NIV and early versions of the ESV translate "flesh" in Romans 6 and 7 as "sin nature". This is a bad translation which stems from a bad interpretation. Thankfully, the ESV has been revised to reflect the true biblical meaning of flesh.
Though we are not all we shall someday be in our totality, thank the Lord that we are not what we were, and that He has given us a new nature with which we love Him and worship Him and fellowship with Him.