Here are some reasons to reject the New King James:

NKJV
Genesis 3:5 For God knows that in the day you eat of it your eyes will be opened, and you will be like God, knowing good and evil.”

KJV
Genesis 3:5 For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil.

“Like God” is different from “as gods”.

NKJV
Psalm 37:3 Trust in the LORD, and do good; Dwell in the land, and feed on His faithfulness.

KJV
Psalms 37:3 Trust in the LORD, and do good; so shalt thou dwell in the land, and verily thou shalt be fed.

“Feed on His faithfulness” is different from “”verily thou shalt be fed”, a promise of God’s provision.

NKJV
Proverbs 18:1 A man who isolates himself seeks his own desire; He rages against all wise judgment.

KJV
Proverbs 18:1 Through desire a man, having separated himself, seeketh and intermeddleth with all wisdom.

Two very different teachings

NKJV
Isaiah 7:14 Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel.

KJV
Isaiah 7:14 Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.

“The virgin” sounds Roman Catholic.

NKJV
Zechariah 13:6 And one will say to him, ‘What are these wounds between your arms?’ Then he will answer, ‘Those with which I was wounded in the house of my friends.’

KJV
Zechariah 13:6 And one shall say unto him, What are these wounds in thine hands? Then he shall answer, Those with which I was wounded in the house of my friends.

Supposing this a prophecy about Jesus Christ, the nails went into his hands (see John 20:25)

NKJV
Mark 16:16 He who believes and is baptized will be saved; but he who does not believe will be condemned.

KJV
Mark 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.

“Condemned” is not the same as “damned”. No form of the word “damn” occurs in the NKJV

NKJV
Luke 11:4 And forgive us our sins, For we also forgive everyone who is indebted to us. And do not lead us into temptation, But deliver us from the evil one.”

KJV
Luke 11:4 And forgive us our sins; for we also forgive every one that is indebted to us. And lead us not into temptation; but deliver us from evil.

Being delivered from evil is anything evil. “Evil one” is a change in teaching.

NKJV
John 5:39 You search the Scriptures, for in them you think you have eternal life; and these are they which testify of Me.

KJV
John 5:39 Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me.

The KJV is a commandment, the NKJV is just a statement.

NKJV
Acts 17:29 Therefore, since we are the offspring of God, we ought not to think that the Divine Nature is like gold or silver or stone, something shaped by art and man’s devising.

KJV
Acts 17:29 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man's device.

“Divine Nature” is different from “Godhead”.

NKJV
Roman 1: 28 And even as they did not like to retain God in their knowledge, God gave them over to a debased mind, to do those things which are not fitting;

KJV
Romans 1:28 And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient;

“Debased” isn’t a synonym for “reprobate”.

NKJV
1 Corinthians 1:18 For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.

KJV
1 Corinthians 1:18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.

“Are being saved” supports Roman Catholic doctrine of no assurance of salvation.

NKJV
2 Corinthians 5:8 We are confident, yes, well pleased rather to be absent from the body and to be present with the Lord.

KJV
2 Corinthians 5:8 We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.

“Willing” is an act of will, “well pleased” is not.

NKJV
1 Thessalonians 4:8 Therefore he who rejects this does not reject man, but God, who has also given us His Holy Spirit.

KJV
1 Thessalonians 4:8 He therefore that despiseth, despiseth not man, but God, who hath also given unto us his holy Spirit.

“Rejects” is very different from “Despiseth”. You can reject something without despising it.

NKJV
Hebrews 2:16 For indeed He does not give aid to angels, but He does give aid to the seed of Abraham.

KJV
Hebrews 2:16 For verily he took not on him the nature of angels; but he took on him the seed of Abraham.

Different teachings. The NKJV doesn’t seem to be in context with surrounding verses.

NKJV
James 4:5 Or do you think that the Scripture says in vain, “The Spirit who dwells in us yearns jealously”?

KJV
James 4:5 Do ye think that the scripture saith in vain, The spirit that dwelleth in us lusteth to envy?

So is it the Holy Spirit (NKJV) or some other spirit (KJV). Again, the NKJV seems to be out of context.

NKJV
James 5:16 Confess your trespasses to one another, and pray for one another, that you may be healed. The effective, fervent prayer of a righteous man avails much.

KJV
James 5:16 Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much.

Faults and trespasses are different.. Some Roman Catholics use this verse as a proof text for the confessional.

This is just a sampling of the many verses I have found in the New King James Version where different things are taught, just by subtle changes. For many generations in the USA, the King James Version was held as the Word of God by a majority of the people. Now, with so many versions to choose from, which one is God’s Word? I’m stating why we don’t use the NKJV. Of course you need to decide for yourself.