Here is what I'm considering (with 8 sensors, 4 front and 4 rear). I only need the audio beeps, don't need to have a visual on the dash and definitely don't want the cheesy looking aftermarket visual aid anywhere in my interior.
https://www.tadibrothers.com/products/parking-backup-sensor-system-with-sound-and-volume-control-tb-s058s
My 2019 Silverado LTZ, which I just traded against my new 2023 Sierra SLE, had park assist and size blind zone detection in the rear view mirrors. My Sierra SLT is high on options, even including sunroof, but has neither of these. Love the Sierra, but was surprised to discover this when I first saw and test drove it.
Here is a video I found on the OEM retrofit, and to me, this cost is not worth it. Keeping it simple.
https://www.google.com/search?q=how+to+add+park+assist+to+2023+GMC+Sierra&sca_esv=577368761&rlz=1C1CHZN_enUS947US947&sxsrf=AM9HkKkQgGbyVPWyIPy6ebBo1_3CDEQkLg%3A1698464984858&ei=2IQ8ZeH_M_Oz0PEPgJeGiAk&ved=0ahUKEwjhy9eQ65eCAxXzGTQIHYCLAZEQ4dUDCBA&uact=5&oq=how+to+add+park+assist+to+2023+GMC+Sierra&gs_lp=Egxnd3Mtd2l6LXNlcnAiKWhvdyB0byBhZGQgcGFyayBhc3Npc3QgdG8gMjAyMyBHTUMgU2llcnJhMgUQIRigATIFECEYoAEyBRAhGKABMgUQIRigATIFECEYqwJI_K4BUM5yWIauAXACeAGQAQCYAaIBoAG6JaoBBTEwLjMzuAEDyAEA-AEBwgIEEAAYR8ICBxAjGIoFGCfCAgcQLhiKBRgnwgIEECMYJ8ICDhAuGIoFGMcBGNEDGJECwgIOEC4YgAQYsQMYxwEY0QPCAgUQABiABMICERAuGIAEGLEDGIMBGMcBGNEDwgILEAAYgAQYsQMYgwHCAhEQLhiKBRixAxjHARjRAxiRAsICCBAAGIoFGJECwgIHEAAYigUYQ8ICBRAuGIAEwgILEC4YgAQYsQMYgwHCAhQQLhiKBRiXBRjcBBjeBBjgBNgBAcICCBAuGIoFGJECwgIIEAAYigUYsQPCAgsQABiKBRixAxiDAcICCBAAGIAEGLEDwgIIEAAYgAQYyQPCAggQABiKBRiSA8ICChAAGIAEGBQYhwLCAgcQABgNGIAEwgIIECEYFhgeGB3iAwQYACBBiAYBkAYIugYGCAEQARgU&sclient=gws-wiz-serp#fpstate=ive&vld=cid:0177bde8,vid:J_fOn3JsNOQ,st:0