I think Titans have a problem allocating all that memory.
Quoted from the Scrypt-jane spreadsheet:
"GPU Memory usage: 2883 MB"
"Seems Kepler Kernal has better memory allocation then the Titan for Scrypt-Jane. Texture Cache set to -C 1 throws an error indicating it fails over to -C 2 but if you launch a -C2 the hashrate is nearly halved."
Edit: Also "Current Titan kernal appears not to allow much more then this before driver soft crashes currently."