Here's the deal, the Sacramento system is really TWO systems; one for the city and one for the county. They have now selected TGs that don't interfere.
In order to get two trunked systems to work in a GRE made scanner, there are several tricks you must do. I am not even sure if the PRO-164 will trunk two sites in the same bank, the last time I tried it was on a PRO-97. It sounds like you have programmed a total of FOUR frequencies in to bank 0, and that has never worked on CC only scanners.
What these scanners do is they look for a (control channel) signal on the first frequency in the bank. Once they do that, they do not even check any other frequencies in the bank set to MOT. This means it could find a signal on the WEAKEST of the two active control channels. Again, it looks for the FIRST, not the best.
The ONLY way to be sure you are receiving from BOTH sites (other than using two separate scanners) is to put them in to separate banks.
I do know that at least one GRE scanner (PRO-96) would handle multiple sites in a system (or even two systems, with the normal TG-overlap caveats) in a single bank - if you separated the sites' CC frequencies with "empty" or "other" (non-MOT) channels. I'm not sure if the PRO-164 will do this, though - I don't have any handy multi-site MOT systems, or even two receivable-with-duck MOT systems, nearby.
In addition to now making them function, you now know which system you are receiving from and can toggle either system on/off easily with bank selection.
If the PRO-96-like method works, you could toggle either system on/off (though not quite as easily) by locking out the appropriate CCs or by putting the two systems' talkgroups into different "ID sub-banks" within the bank. You'd still be able to recognize which system you're hearing, since the PRO-164 shows the alpha tag of the current CC when it's receiving a voice call on a trunked system.
... time passes ...
OK, I've verified that the above
does seem to work on the PSR-300 family (the PRO-164 is a RadioShack-badged PSR-300). I put my PSR-300 on the discone, with this in bank 0:
* 800MHz MOT CC for local system in channel 000, labeled "CC1"
* "Dummy" freq in channel 001 (25.000MHz, CTCSS=131.8)
* 400MHz MOT CC for a distant system in channel 002, labeled "CC2"
* Two sets of base/offset/step settings for the 400MHz system
* TGs for the local system programmed
* Bank in "Open mode"
I get my normal "local traffic" on the 800MHz system, showing me correct talkgroup IDs / tags as well as the "CC1" tag. I also get a bunch of noise from the 400MHz system - brief pulses of audio, showing "CC2" tag and the correct voice frequencies... but it's a digital voice system (San Mateo County, CA), so the voice behavior is quite erratic.
Bottom line: If you have two Motorola systems, or two sites on the same Motorola system, you should be able to program them into the same bank on a PRO-164, just like we've done for years on the PRO-96. There are caveats:
* the same set of programmed TGIDs are used for both, so it's best if they don't overlap
* you cannot mix two VHF/UHF systems, unless they use the same set(s) of base/offset/step