Just replaced a double kitchen sink with a large single sink. Reinstalled the same garbage disposal to the single drain. While both sides of the old sink drained just fine, the new sink is slow to drain. Any tips? Perhaps some type of vent? Thanks!

You should be vented from the old installation. A simpler explanation might be that while installing the new sink you disturb some mineral build up in the drain pipe and now you have a partial clog.
The solution would be to remove the "J" bend from the trap and send your snake up into the wall, (see image).
You will hit a bend about 8 inches in but once past that you only have about 5 more feet to go. After, flush with a sink full of hot water. Good luck, Tom

I agree but try this before rodding. After you remove the trap put a bucket under the disposal drain and pour some water down the sink drain. Does it drain faster or the same?

Well, after a little more observation, I determined the cause to be a restrictive back-splash guard (my term for the rubber insert in the disposer inlet). After trimming about half the length of every other rubber finger, it drains just fine.