Here in the printer’s manuscript, Hyrum Smith initially wrote an intrusive of (“with all the power and of faculties which I have possessed”); almost immediately Hyrum crossed out this extra of. However, the 1837 edition accidentally reintroduced the of, not as an extra word but in place of the preceding and, thus “with all the power of faculties which I have possessed”. The 1908 RLDS edition restored the original and to the RLDS text, probably by reference to 𝓟. In the 1920 LDS edition, the original and was restored to the LDS text, probably by reference to the 1830 edition.
The most reasonable source for the tendency to write of after power is because power of is so frequent in the text (occurring 153 times in the earliest text). The original use of and in Mosiah 29:14 is clearly supported by Nephi’s parallel language in the small plates of Nephi:
1 Nephi 15:25 Mosiah 29:14
yea I did exhort them and even I myself have labored
with all the energies of my soul with all the power
and with all the faculty and faculties which I possessed
which I have possessed that they would give heed to to teach you
the word of God the commandments of God
Semantically, the reference to energies in 1 Nephi 15:25 parallels the use of power in Mosiah 29:14. And in both passages, the first noun phrase is followed by a conjoined noun phrase that refers to the faculties that the speaker possesses.
Summary: Maintain in Mosiah 29:14 the original reading “with all the power and faculties which I have possessed”.