Audio Sync Problem

I'm a newbie to Resolve and have been trying to use the software to sync external audio to a video/audio source. In these cases, I'm using a better version of the audio track from the same performance. Once I visually align the waveform (the new audio against the old) at the beginning of a track, the audio begins to creep out of sync for the duration of the track. All of the audio are entered as 48kHz. I've also set the project settings to the same frame rate (e.g., 29.97fps). This makes my syncing projects very challenging and time consuming. If I were to fix this by a series of cuts and slides, it would require about 12 cuts per 4-minute track. I realize that I'm probably missing something. Any ideas? Thanks!

What cameras were used for filming?

What field recorder for audio?

(Was timecode set up?)