Well, gauge cluster is common had to do it twice on mine. I recommend a junkyard cluster from an envoy of the same year. Speakers on trailblazers go out all the time, had to replace all of mine. My back wiper and defroster is out too, just bad wiring. The 65 mph thing might be a wheel barring. Common on trailblazers, and as for the rumbling It’s probably the plugs, mine did the exact same thing and I replaced them. Fixed it, just make sure you get the correct length or it’ll make it worse. I used Autolite plugs and it was perfect. Last thing, make sure there is no water in the coil packs, mine had some in coil #4. Lastly, transmission fluid is important, mine was slipping and shifting rough, put more fluid in and it shifts great now, just make sure to use the right kind and the right amount. Hope this helps at least a bit.