I will use an image from my e-sword translator for this. Since it can be difficult to post the Hebrew needed to properly covey what I need to make my point. In Hebrew, the symbol used is for the word in question contains the horns of an OX, which means Strength: The strength of the ox.
A masculine noun meaning a rock. It refers to a large rock, a boulder (Jdg 6:21; Jdg 13:19; 2Sa 21:10); a cliff or wall of rock (Exo 17:6). It is used in figurative expressions: honey from the rock, from rock clefts where some bees lived (Psa 81:16 [17]); of Abraham as the ancestral rock of Israel (Isa 51:1); of a rock as a symbol of stability (Job 14:18; Nah 1:6); of God as the Rock to look to and depend on (Psa 31:2 [3]; Isa 17:10); of a rock personified, e.g., as Israel (2Sa 23:3); of God as the Rock many times (Deu 32:4, Deu 32:18; Hab 1:12). It is used of an insufficient rock, a god of the pagan nations (Deu 32:31). The word rock was often used a a symbol of strength and stability. Thus the NKJV uses the word rock to show strength. The idea is taken from the fact that a lofty rock or fastness was inaccessible by an enemy, and that those who fled there were safe.
Thus throughout the Old Testament the word Rock is used often times to describe GOD's immutable power and strength, and Jews of the early centuries used Rock often as a metaphor for GOD, as in HE is their strength, their ROCK which is immovable.
The original KJV worded the passage for Isaiah 44:8 as thus'
"""Fear ye not, neither be afraid: have not I told thee from that time, and have declared it? ye are even my witnesses. Is there a God beside me? yea, there is no I know not any. """"
However, in translating the OT Scriptures, the authors of the KNJV used a word more closely associated with the way the Jews looked at GOD as a Rock. Thus we read the NKJV for Isaiah 44:8 as thus;
"""Is there a God besides Me? Indeed there is no other Rock; I know not one."""
Even the more accurate word for word translation, (As close as one can actually get) the NASB uses the word Rock also. Interestingly, the NKJV is considered more closely to the thought of the original language to which both the NASB and the NKJV both use the word rock in Isaiah 44:8.
Thanks for making me do this in-depth look into translations. It was fun. I pray my answer did more than just confuse you.