What pickup were you replacing? The SSL5 should be a good bit darker/middier than a regular output single coil. If you had a single sized humbucker, it's might well be brighter than that though.
As far as thin sounding pickups, playing with pickup height can make a difference. If you lower the whole pickup you will slightly soften the attack of the pickup (if the problem is that it's kinda barking too brash/loud). If it's too low you sometimes lose bass though, so give raising it right up a try as well. Also if you raise the bass side of the pickup a little higher than the treble you'll get more response from the bass strings, which can make a bright pickup sound a little more balanced to the ears.