Are the KJV, Textus Receptus, and Majority Text the same?

No, these three are distinct, though they share some overlap. The Textus Receptus and Majority Text are very similar but differ at hundreds of points[1], and the Majority Text differs from the Textus Receptus at about 1,800 places, including some where the Textus Receptus reading is not the majority reading[2].

The Textus Receptus is the oldest of the three. Erasmus compiled and edited it in the 16th century using several Greek manuscripts that were eastern/Byzantine in nature[1]. It was based on a very limited number of manuscripts, all eastern and dating to around the 12th century[1]. When Erasmus first published his printed Greek New Testament, he had only eight manuscripts to work from—three of the Gospels, four of the Epistles, and only one of Revelation, which was missing its ending, so Erasmus created his own Greek version by translating the available Latin version backward into Greek[3].

The Majority Text emerged much later as a different methodology. It is compiled by taking the simple majority of manuscript evidence to decide which variations to use in the Greek text[3]. While the Textus Receptus is based on a particular small set of manuscripts, the Majority Text is based on giving every manuscript a vote[3].

The King James Version is based on the Textus Receptus, not the Majority Text. The King James Version and New King James Version are based on the Textus Receptus[1]. The translators of the King James Version integrated their available manuscripts with the then current published edition of the Greek New Testament[3].

Importantly, fully eighty-five percent of the New Testament text is the same in the Textus Receptus, the Alexandrian Text, and the Majority Text[4]—so while they differ at specific points, substantial agreement exists across all three.

[1] Got Questions Ministries, Got Questions? Bible Questions Answered (Bellingham, WA: Logos Bible Software, 2002–2013). [See here, here, here, here.]
[2] Charles W. Draper, “Textus Receptus,” in Holman Illustrated Bible Dictionary, ed. Chad Brand et al. (Nashville, TN: Holman Bible Publishers, 2003), 1578.
[3] Stephen De Young, The Whole Counsel of God: An Introduction to Your Bible (Ancient Faith, 2022), 86–87.
[4] The New King James Version (Nashville: Thomas Nelson, 1982). [See here.]