I might be buying a new truck, and the guy said the thermostat is sticking, is this a problem to worry about? If so how much does it cost to replace or fix, and how difficult is it to do?

 

t-stat's are easy to change... but you might want to bring it to a shop and have them check for a leaky head gasket. I'd guess that it's overheating, does it overheat when you 1st start it up? that could be a sign of a stuck t-stat... anything else, have it checked out 1st.

head gaskets are easy to change on the ram, just time consuming.