I hope this can be answered, but does slip still scale with training in stealing?

Slip has never had anything to do with stealing. It's directly proportional to the amount of strength you have (how HEAVY you can slip), and agility (how LONG an item you can slip). This is also affected by hindrance, which affects far more than it should for stealthers, and not enough for everyone else IMO.

Monster Elec

You hear the distant echo of a savage Horde snarling in barbaric disapproval of your deeds.