A vacuum leak can cause high rpm, stuck throttle linkage can cause this as well Oil change will not fix high idle problem. Overdrive is a term for one of the gears in your transmission, you may have a button to turn it on and off? Basically it is a gear that will give you better fuel economy at cruising speed. Need to have it brought somewhere, high rpm cannot be that good for transmission when shifting from Park to Reverse or Drive.

It means your oil filter is getting clogged up with build up of dirty oil. Take your car to the dealership and have them replace the oil filter with a clean one and have them drain your dirty oil and replace with clean oil as well. The lower RPM while driving, the better, higher RPM while driving means your car needs service. For example, I'm driving a constant 75mph and my RPM is between 1,500 to 2,500, my car is running smoothly, however if I'm driving a constant 75mph and my RPM is between 2,500 to 3,500, my car is using more gas to push the car and needs service ASAP

You need a new idle speed sensor inside the front of the throttle body! They are very simple to change IF you have a $12.00 set of tamper-proof Torx bits. Mine came from Car Quest.

Go to the GMC/Chevy dealership and ask them to show you what the overdrive is and how to use it. This will not cost anything.

Park and call AAA, AA, or NA. But I think GM is your best bet.

also my oil light is on, do u think if I change the oil it will help?

So my 2005 envoy v6 has been running at a very high rpm as of late, it runs at 3500rpm to stay constant at 50 mph, this is draining my gas I assume, what is the problem and no my engine light is not on and I don't know what this "overdrive" thing is I keep reading about