I was under the hood for something unrelated and noticed the coolant level in the reservoir was very high. Truck had been sitting all day and was cold and I haven't had any overheating issues. Any ideas what's going on?

 

When was the last time you serviced (flush, added, drained, anything) the coolant?
When is the last time you checked the coolant level and what was it?

 

who was the last person to add coolant to the reservoir? could have been a mistake

 

I want to say I had a coolant flush and fill around 40K. I'm at 86k now. Anyway I siphoned out the extra to get at the top line of the cold fill level and drove to work. There was some natural expansion when I got there. 8 hours later I checked it before leaving and it was back to that top line. I guess I just need to keep an eye on it so it doesn't become a bigger problem.