I have been looking for slimes in my LP game and realized that I have only found 1. So I went online to find slime chunks (via http://chunkbase.com/apps/slime-finder) and then proceeded to find 2 slime chunks and then cleared out entire chunk between y = 34 and y = 40+ (ceiling varies in height) after about 7 days (IRL) I checked and found no slimes. The chunks are just below my base where I spend nearly all my time and only about 32-80 blocks beneath me depending on my whereabouts.
The rooms are lit in the floor, one chunk with jack-o-lanterns, the other with glowstone.

I have also found a swamp biome and killed all mobs on the surface during all moon phases (except new moon) and never seen a single slime.

My seed is : 1174088847753350200
worldtype : default,
structures on
gamemode : survival
difficulty : hard (non-hardcore)

Swamp at around -209 64 238 biome : swampland
Slime chunks at 192 35 208 -> 207 35 223 (Chunk 12/13) biome: plains
and at 144 12 176 -> 159 12 191 (Chunk 9/11) biome : beach

I haven't found any other swamps to compare against.

This world was started I believe in 14w02a (the new andesite blocks were already generated in my world)

In the nether I have had no difficulty finding magma cubes, they spawn everywhere it seems.