After months of learning and small tests around the neighborhood, I've reached the conclusion the transmission needs to be replaced. The main issue is a mechanical grinding noise whenever the RPMs get above 900RPMs. Once I reached the conclusion the transmission had to go, I put the car back up on car jacks, removed the back wheels, and the bumper to prepare for the major change.
I looked into replacing the automatic transmission with a manual transmission. I priced out the manual transmission and all the supporting equipment (clutch lines, clutch pedal, shift cables, shifter, console, longer transaxles, etc.) and the total ranged about 4-5 times the price of a used automatic. Once I figured out how expensive it was to convert, I turned back towards just replacing with another automatic.
Today I ordered the new transmission. While the car is up on jacks, I'll also install the Orion BMS system and try to get the 6 remaining batteries mounted. More to come when the new stuff arrives.