Lately I've noticed my toyota rav4 takes a while to warm up, and once it's hot, the temp still fluctuates a bit more than I'd expect, it gets worse in traffic and uphill slopes, its not overheating thankfully, but definitely not as stable as it used to be, can anyone on here relate?, and can I improve temperature control, seen something about a temperature thermostat somewhere but I dont really know how it operates, but is it something that can pass as a good reco for this current issue?