Most disposers last eight years.
After that, the blades start to dull and it leave too big of chunks.
Those larger chunks will finds ways of plunging the holes in the disposer and the baffle in a baffle tee.
So think about it, how long has the disposer been there, has it ever been changed?
I find it a standard policy, that every eight years, the sink gets a new set of blades.
I like Insinkerator.
Easy to install, good pricing.
Even the less expensive ones work pretty well.
And their higher end stuff is so quiet. I love those.
Do not buy a Costco disposer.
If you run a dishwasher into the top of the disposer, the inlet on the Costco Titan disposer is too small and it backs up the air gap all over the counter.
The Costco disposer has got the be the lightest weight disposer on the marker. Can they make if out of flimsier parts? I don't think so.
Terry Love

It's not your disposer, but a partially clogged drain. You might want to remove the trap and clear the line with a snake. If it's greasy residue coating the line, might take extra effort to scrape it loose.

Terry, you mean to say that the dishwasher drain inlet isn't a standard diameter? Interesting.

Any maybe his argument on the disposer makes sense. But I'd check the drain line anyway.

Most dishwasher inlets at the top of a disposer are the same size.
Insinkerater, Whirlpool have always been good.

It's only on the Costco Titan disposer that I've seen an undersized inlet.
Terry Love

The problem may not be nearly as bad as what has been described above.
First off, when you look down the throat of your disposal you cannot see the cutters. The two movable pieces that are commonly believed to be cutters are actually "Slingers". The slingers are attached to the top of the cutter wheel by means of a pin that will allow the slingers to rotate freely, although generally with age they often become stuck in one position and even when that happens it is not a problem.
If you look around the outer circumference of the rotating cutter wheel you will see a slight gap between the edge of the cutter wheel and the inside of the disposal body. You will also note a series of vertical half round groves on both the outer surface of the cutter wheel and the inner surface of the disposal body. The reslutant gear tooth effect on both the cutter wheel and the disposal body is what comprises the cutting effect. As the wheel rotates the slingers are held pointing outward by centrifical force and as foodstuffs enter the chamber the slingers literally sling the foodstuffs out against the inner wall of the disposal chamber. The foodstuff is then drawn down in the space between the cutter wheel and the disposal body where it is shredded apart by the gear tooth projections of the cutter wheel and the body.

On the discharge side of the disposal body the discharge port is diretly in line with the edge of the cutter wheel, in fact, if you remove the discharge line you can see the edge of the cutter wheel and the vertical cutting grooves on the cutter wheel circumference. As the food is ground between the cutter wheels and the disposal body it is also carried around to the discharge port, where is is now slung out into the drain line by centrifical force in nearly the same manner as a cenrifical pump.
In the original post they stated that they wash dishes in that sink but rarely use the disposal. In that case, when the dishwater is discharged through the disposal the water passes through the narrow gap between the cutter wheel and the disposal body before going out the drain line. In the course of time the cutter wheel and disposal body will coated with a layer of cooking grease and micro fine pieces of foodstuffs from the dishwater.
Properly, whether you use the disposal to grind vegetable waste or not, you should run the disposal a few moments every time you dishcharge dishwater, especially when dishcharging dishwater after washing the pots & pans.
Unfortunately the grease has already built up to a point where it is starting to present a problem, but their is a very quick and easy solution. Toss a handful of ice cubes in the disposal, turn the water on, then turn the disposal on until you have ground all the ice cubes. Not only will that reduce the grease buildup and improve the drain function, it will also help eliminate odor which results from decaying foodstuffs caught in the dishwasher.
Try the ice cubes a couple times and you will probably find yor drain is once again draining correctly and won't require taking pipes apart.