1997 Chevy Blazer (4x4) is having major issue with low power when taking off.

I recently changed the Front and Rear Differential Fluids, as well as drained the transmission fluid with a new filter.
I am the third owner and have no idea when these were last changed.

After finishing these fluid swaps, I went to go for a drive to make sure everything was working fine and it's not...
When accelerating from a stop, the engine revs very high but the vehicle barely moves - pedal to the medal and it goes like 10mph at the most. Going in reverse is normal, and once up to speed there seems to be no issue.

I will admit that I didn't put limited slip additive to the differential fluid, and it doesn't say that it has any already mixed in. (I used STP brand 80W90)
I tried looking in the manual to see if it's needed but I couldn't find any references to it.

Any ideas if that's the issue?