I'm restating a lot of the above, but I'm also adding some perspective for you, i.e. why you should care/act, on many of these recommendations.
As all folks have recommended, change ALL fluids, as you really don't know for sure just how old they are, or if they were the correct ones to begin with. Thoroughly visually and by feel analyze the fluids, as you can often see potential signs of future issues by just looking at, smelling, and finger-squeeze toughing the fluid and any particles that may have come out with the fluid. Lots of members here periodically send a used oil sample to Blackstone Labs for analysis, as the results can tell you a lot about the health of your motor.
IMO,
@B-train gave your one of the best pieces of advice off the top. To the extent possible, use ONLY GM Genuine parts. Aftermarket parts, particularly if they have any electronic components within them, often do not play well with these GM trucks and their CanBus electronic communication system. Your truck is at the age where GM has already started discontinuing replacement parts, so sometimes, you will be forced to go aftermarket. Check with us first to see what Members' experiences are with specific aftermarket brands of parts, when you hit that replacement situation, so that you don't have to make the same replacement twice.
AFM Delete - If nothing else, get the AFM tuned out of your control systems. The best option would be to also get the mechanical delete of AFM engine components, but that will run you $5k+, so the budget needs to be assessed. The AFM hardware often fails sooner than non-AFM hardware, and a failure of this kind will definitely take out your cam, and potentially incur other catastrophic motor killing damage.
As
@swathdiver recommended, check out your Z95 Magneride suspension system. IMO, this is an elite suspension system, but like all other maintenance parts, they eventually fail, generally around 80k - 100k miles. At your mileage, the struts/shocks in this system should have been replaced, but from what I've seen in the market for these trucks, when sold used, these components have already failed, but have not been replaced. When you start your truck, after it sits overnight, listen on the outside near the driver's side rear wheel. Within 5 - 10 seconds of startup, you should hear the air compressor fire up to 4 - 8 seconds. If you do not hear the compressor fire up, chances are that your Z95 system is not currently fully operational.
As
@thefrey recommended, check/monitor your oil pressure at the status marks that he recommended. Good oil and oil pressure are the life blood of these 6.2 motors, so there must be clean oil at a solid oil pressure, to ensure that the motor lasts for 200k+ miles. The O-ring on the oil pump pickup tube is a common failure point on these motors, so if you see a hot idle oil pressure below 20 psi, there is a good chance that your O-ring is failing, and needs to be replaced.
As
@mikez71 recommended, check out the motor mounts, as your truck has liquid filled bushings within the motor mounts, and these fail and are a maintenance item. The liquid was meant to further reduce engine vibration in the main cabin, but IMO, there is no appreciable difference in reduced motor-related cabin vibration with these OEM motor mounts. If you need to replace them, I recommend that you replace them with H3 motor mounts, and you will never need to replace them again.
As
@thefrey recommended, replace the heater hose Tees, located at the firewall on the passenger sire of the engine bay. These plastic Tees WILL rupture, and it will happen at the most inconvenient time, and dump most of your coolant out within 30 - 60 seconds or less. While you are making that changeout, replace ALL of your radiator and heater/coolant hoses in the engine bay. Most likely, they are original (the manufacturing date is typically stamped on them), and they definitely deteriorate over time from both the engine bay heat and the corrosiveness of the liquid that they are carrying. I know, as it happened to me. If you personally change out the tees, be sure to wear gloves, as the firewall insulation is quite aggressive, and your hands will itch for days.
Both
@SpareParts and
@thefrey recommended getting a tune on your motor and transmission. GM tunes are OK, but they are like purchasing all season tires. They are OK for most situations, but not really very good or great for any one situation. The GM transmission tune gives a smoother transition through the gears, but definitely at the expense of the longevity of the transmission. A tune of both the motor and transmission, say from
@BlackBearPerf (BlackBear Performance, which a lot of Members use), will definitely wake up the motor and add longevity to the life of your transmission. At ~$700, you may say that this is definitely discretionary, so it really depends on how you want your truck to perform while driving it.
Be aware that the GM torque converter is a weak point in these trucks, and when it grenades, it will take out your transmission as well. Look for any particles when changing out your transmission fluid, as this could be an early sign of an impending torque converter failure.
Do you have, or have access to, a quality bi-directional scanner? If not, I recommend that you get yourself a quality bi-directional scanner (~$500) to add to your tool box. Then, you will be able to read ALL trouble codes, along with a brief explanation/pointer to the source of your issue. You can test many of the truck's electronic functions with the scanner, in order to determine the source of an issue. You will also be able to reset/delete trouble codes, after taking corrective action. You will literally save thousands of dollars in diagnostic and repair costs over the life of your truck, and you will most likely recoup the cost of the scanner within 1 year.
These are wonderful trucks, and if you are good to them, they will be good to you.
