We recently put in a new kitchen sink going from 2 divided basins with a drain on one side and a garbage disposal drain in the other side. Using the exact same garbage disposal on the new sink, when large amount of water get dumped into the sink (emptying water from bowl) the water becomes very slow to drain if at all.

I verified the drain has a vent under the sink so I don't believe I am just removing the air gap. Through brief research online suggest the garbage disposal flaps may need to be cut back to allow more volume through though I'm a bit cautious as I did not have this issue with our dual basin sink.

Anything else I should be considering here?

Venting issue is what it sounds like.
Is the aav clogged!

You verified that the p trap is clean ?

Also kitchen sink drains are notorious for building up from grease/food so I would pull the trap off and run an auger through the wall to verify it is clear

When I put this in, I ran an entire new ptrap so I know that is good to go.

Whoop Delecto said:

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Not related, but review the dishwasher installation instructions and pay attention to the drain line, I believe you need to elevate the hose loop under the sink.

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You are 100% right, when I inspected the p trap a bit ago I fixed the drain line so that it drops into the disposal as opposed to rising to it.

Most of the new dishwashers have this loop built into them

ForeverAg said:

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Through brief research online suggest the garbage disposal flaps may need to be cut back to allow more volume through though I'm a bit cautious as I did not have this issue with our dual basin sink.

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Easy way to test this....I know when I dump a full pot of water, etc. in our sink it's slow to drain as well. If I simply push down the garbage disposal flaps it flows out normally/quickly. Never thought about cutting them back, easy enough to just open them up slightly when it does happen.

I'll test it tonight because now I'm curious. The AAV is behind the sink and in a really bad place for me to try to remove it now so I hope it hasn't been clogged this whole time and by having the 2nd sink it acted as a secondary breather.

My disposal side of the double sink does this occasionally. In fact its done it in every house I've owned.

Just flip it on quick and it will flush everything down the drain.