I agree with hank, it could be the temp sensor and would still suggest that you have it serviced especialy since you don't have any service history on it. Chances are goo that the first owner had the 30K done, since it was free, but you never know and at 50K you are close enough to the next service anyway.
As a side note, since you have no history on this truck, consider doimg the 60K early and make sure you have all the fluids done including the power steerin and brake fluid then as a new owner you can sleep better at night not having to worry about it.
Good luck,
mike J.