Rough Idle when coming to a stop

Poor fuel quality could cause it. Those engines can be a little picky. It also could just be time for new spark plugs and wires. When was the last time that they were replaced? And what were they replaced with? Anything other than OEM quality stuff in those trucks could be causing that.

Misfire code is probably p300 (random multiple misfire). Very common among all cars.

With a leaking intake gasket, you could be getting a little water into the cylinders, causing the miss, among other things. Also, I would wonder what the plugs are exactly. Just because they look okay does not mean much if they are not strong enough to begin with. Plus if there is water present inn the cylinders, it could be cleaning the plugs, making them look better than they are.

I have more to say, but my toddler just woke up from his nap. I would still say to find out exactly what plugs and wires were used. Low quality ignition system parts can really make your car run like crud. I will get back on here later.

You do not necessarily have to change them, yet. Just check them and let us know what they are. If you want, you can take pictures of them and I will look at them on here. Also, get pictures of the contacts in the ends of the wires. And look to see if the wires say 7mm or 8mm on them. It will be in the text on the wires.

I'd go ahead and change those plugs. If the wires were done 2 years ago, then I wouldn't do them if they look ok (not cracked, exposed, or melting). California cars do have some specific differences that allow them to pass stricter emissions requirements, but I've never heard of them requiring a different plug.

Here's an ebay link to the plugs that are stock (I think). http://www.ebay.com/itm/8X-ac-delco-OE-Spark-Plugs-Chevy-Pickup-tahoe-sub-5-0-5-7-vortec-96-97-98-99-/252808374538?epid=2231691670&hash=item3adc8da90a:g:3FEAAOSwax5YxDir&vxp=mtr

If I was you, I'd get the part number from the listing and call the local Chevy dealer to make sure that these are a fit for the job. Then order them. Much, much cheaper than buying from the dealer or local parts store.

As for the oil leaking onto the O2 sensor wiring, I don't think it's causing an idling issue, but you should either fix the leak or find a way to protect that connector.

Last thing, maybe I asked this before. but I can't find it in the comments. Is the service engine light on? If so, have you had it scanned recently?

Yeah sometimes it can be hit and miss. Just to be certain, P0154 and 174 are pointing to an issue with bank 2, sensor 1. That's the sensor on the exhaust manifold on the passenger side of the engine.

I did a quick google search to make sure I wasn't missing anything, and came up with this article re: P0154. https://www.obd-codes.com/p0154

Read it. In particular, look at the "Causes" section. You'll see that oil or water getting into the connector could be causing an electrical short and causing the code. I'd probably pull the sensor and clean out the connector. Put it back in, and then either fix the oil leak or find a way to protect the connector (maybe put a piece of rubber hose over it or something like that). Then clear the codes and see if it's any better. Go from there.

I have my doubts, but I suppose it's worth a shot. Get some of the Lucas fuel system treatment and a can Mass Air Flow (MAF) sensor cleaner. Here's our how-to guide on that: https://www.2carpros.com/articles/mass-air-flow-service

Your truck is going to be little different than that, in that you'll have to open up the air cleaner box and take the sensor out (because the sensor is a section of the tubing going from the air cleaner to the intake, if my memory is correct). Then you simply spray the MAF cleaner in the same direction that the air normally flows (from the air cleaner towards the intake). Then just let it dry out for a while before plugging it back in and putting it back together. A few hours should do it. Whatever you do, do not physically touch the element, because it's really easy to damage.

Also, while you're in there, it might be worth putting in a new air filter, or at least taking the old one out and beating as much dust out of it as possible.

Well both codes do point to issues with Bank 2, O2 sensor 1. That's the one on the exhaust manifold on the passenger side of the engine. Before actually replacing it, be sure to take a good look at the wiring going to the sensor, as well as the connector itself. Problems there could be causing your issue.

Here's our guide on replacing an oxygen sensor: https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

Awesome! I'm glad we could help you save some money. Please feel free to use this forum any time.