Although the tag should not affect gapless playback, I've heard rumors that VBR will screw it up.

Just as an experiment, take that set of wav files and encode them all on the same command line (all on the same command line simultaneously is one of the requirements for the nogap parameter to work) with NO OTHER PARAMETERS other than --nogap. Don't tag them, don't VBRfix them, don't do anything other than just run them through lame with nogap. Then squirt them into the player.

See if that works. The end result will be that lame uses all of its defaults which I think is 128kbps FBR.

If that works, then try changing one thing at a time in your procedure, re-encoding and re-testing each time, until you find the one thing that breaks it. Then report back here.