I bought a used TI-nspire with 84+ keyboard specifically to try rpn83p, as they are $10 less on the auction site than the 84+ itself. Mine was running OS 2.54MP. The MacOS "TI Connect™ CE" program recognized the calculator as an unknown device, and there was no way to designate it as an 84+. Attempting to install rpn83p failed, giving an error after a few seconds. An OS upgrade to 2.55MP just sat there with a spinning wheel for 30 minutes before I force-quit (and probably wouldn't have fixed anything anyway, even if worked).
The solution was to install tilp2 on a Linux machine. That program recognized the calculator as an 84+, and by using it rpn83 installed flawlessly in under a minute.
I'm posting this as an "issue" for the benefit of any others in the same situation. Thanks for the program! Now I get to play...
EDIT... the precise error message received was:
"Hello? Unfortunately, it looks like Unknown Device - 9C81 has stopped talking to TI Connect™ CE. Reconnect and retry the transfer. If this keeps happening, contact TI for help."