I was looking around the internet and found a listing for a Futaba FP-TP-FM module and a Futaba FP-TK-FM module. What's the difference and what radios are the different modules for? I couldn't find any info. about the modules.

Futaba FP-TP-FM FM Transmitter Module 72MHz (high band)
Futaba FP-TK-FM FM Transmitter Module 72MHz (low band)

The "TP" modules are for the 7U, 8U, and 9C-series transmitters. The "TK" modules are for the 9V and 9Z-series transmitters. You can use a TK in lieu of a TP module, but you cannot use a TP module where a TK is called for.