Owners manual:
https://cdn.dealereprocess.org/cdn/servicemanuals/chevrolet/2018-silverado1500.pdf
Your going to get a million and one different opinions...
I would test the shocks to see if they need to be replaced. Body mount bushing's can have a big impact on comfort/feel of the vehicle, and they may be dried out (like mine were).
I use acdelco oil filters, but I really hate how the threads of the filter have substantial burring on them.
I think most people here would agree oem spark plugs are your best bet. As to whether or not you should change them, "use your judgement. How does the engine perform, idle etc.
I use the gm recommended washer fluid. My last truck I used standard -40 fluid, and over time it built up film on the windshield that just did not want to come off. Differences in type of alcohol/content I guess
I like the gm wipers
Nothing wrong with the oe air filter.
I would replace the cabin filter yearly. They pack up with debris fairly easily. Look for one anti-microbial, your truck will smell better for it.