Yes, it is a 123 code, hang a new sensor and stuff in a new thermostat while you are in there. You will find that you need to pull the upper thermostat housing to get to the temp sensor anyhow. On your slow crank, have you tried cranking it with a set of jumper cables hooked up to another running vehicle? If your connections are good on both sides of the circuit, positive and negative, then I would say you have a weak battery regardless of what the guys at the local parts store tell you. The only other thing that you can do is to hook up an inductive ammeter to it while it is cranking and see what kind of current it is pulling. Off the top of my head I would say that something in the area of 400 amps should be about right but if you are pulling in the area of 600+ you might want to see what is causing it. Bad starter or somekind of mechanical drag on the engine like a seizing piston or crank (not very likely)

Mark