Dave, in those cases, have you tried using non whole numbers for the bpm? when i was using an external drum machine for a click, it was always steady (didn't fluctuate), but it was some odd # (EG) 120.54567 bpm
for all... this is where it helps greatly to have a click audible at the start and the end... makes it easier to compute the actual bpm. and leave that count-in (count-out) untouched... no reverb, compression or any fx. this means no fx on the master bus when exporting seperates. keeping it dry/untouched makes it very easy to visually line up the clicks because the wave form will look exactly the same as the original. if you insist on using fx on your seps, only use it on the individual tracks, not the master.
i know it can happen, but i've never experienced a tune that was tracked to a click that (unintentionally) changed tempo throughout the song... no matter what format was used.
raises a red flag when people say things like... "i had to slice and move it every 8 bars to get it to fit the tempo/grid." this tells me they're using the wrong tempo in their software compared to the track that's being lined up. possible reasons... either the person recording the track (unknowingly) changed the tempo of the original or the producer is trying to force fit an odd bpm (120.9487466) into a standard bpm (120)