This may be a difficult problem to locate. It sounds like there is a poor electrical connection in the circuit for the speedometer. There is a speed sensor on the transmission, the speedometer and the wiring in between them and the problem can be with any of these.
If your cooling fan motor keeps running, you will want to disconnect remove the fuse (40 amp fuse in the battery junction box) to keep it from draining the battery. It's likely that the CCRM (Constant Control Relay Module) is bad and keeping the fan on.
At this point you should have the codes checked to determine why the check engine light is on.
Check the fuse #3, and if it's OK, then you will need a wiring diagram to diagnose the circuit for the running lights.
Look on the bottom of the radiator, there may be one there, or there may be one on the engine block. You can also remove the bottom hose from the radiator for a few seconds to allow some of the water to drain out.
Your Blazer didn't come with a cabin air filter!
I don't have the maintenance chart for the 2007 Sebring, but if you look at the parts that are actually replaced at the 60k service, that will give you a good idea as to what is most important, as well as an inspection of the brakes, belts, hoses etc. Your owners manual should have the maintenance chart.
The torque for your flywheel is 80 Nm (59 ft. lbs.). Make sure you tighten them in a star pattern. Here is an image that will help! Copy and paste this link! www.explorerforum.com/photopost/data/500/lugTorque.jpg
It's very likely that the head gasket is your problem. These gaskets often leak if the engine has been overheated, but can occur on an engine with high mileage too. The next step is to have a shop remove the head(s) and inspect the head gaskets.
Many vehicles have a shift lock mechanism that is "un-locked" when you depress the brake pedal, is it possible it is related to this feature?