Can you please describe the antenna types and how they're arranged on the tower? Are these three radios sectors installed to provide 360 deg coverage?
The main benefit to GPS sync is the ability for radios in a back to back orientation to take advantage of frequency reuse, e.g. the ability for both radios to use the same frequency. There are a few requirments to this however:
1. The radios ideally should be back to back (180deg apart)
2. The distance, uplink/downlink ratio, frame size need to be set the same, and the 'front radio, back radio' settings need to be set.
3. The antennas being used should have a high front to back ratio. If you're using Cambium OEM antennas you're good to go.
4. And the most important part, clients from either sector cannot hear the opposite sector.
Assuming you're using (3) 120deg sectors on a tower to provide 360deg coverage, you won't be able to effectively use frequency reuse because clients from one sector will most likely be able to hear the other sector(s) as these radios are not 180deg apart.
For further information and tips on GPS sync and frequency reuse with ePMP, check out this knowledge base article.