Amber,
It's hard to say what is wrong without seeing what you did.
If you mean that the drain from the p-trap angles down very steeply before it reaches the vent, then I would see a problem. Using an air emitter like the Studor vent will help to break the syphon effect.

If you mean that "after" the vent, it drains steeply, then snaking is likely the answer.

Terry Love

: i recently replaced most of the plumbing in my kitchen. when i did, the "T" in my kitchen drain had to be replaced at a slope greater than 1/4" per foot due to other obstacles. it now has a slope of appoximately 4" per foot. it used to connect to the vent pipe about a foot or so higher than it does now. could this be a reason for a very slow-running drain? running the water for more than 1 minute forces it to back-up into the sink. i'm going to snake my vent pipe, but should i be looking at this slope as a potential problem?