I can't speak for the Specialized tubes, but I've been using Slime tubes for over four months, including in temperatures below freezing and haven't felt any inbalance, or noticed any thickening. The only minor problem I've had with them was a clogged valve, but that was my mistake in pumping/letting air out with the valve at the bottom of the rim rather than the top. From people I've spoken to Slime seems to work fairly well for MTB pressures but not so well for Road, but that's just a sealing thing.

It sounds like Specialized use a different formula to Slime.

Richard