oes po125 & po 305 mean on 98 chevy silverado mean

Question

What do these mean and how would i fix it

Answer 1

P0125 the thermostat may need to be replaced if there are no leaks or low coolant level.

P0305 is a cylinder 5 misfire, could be a spark plug or wire or ignition coil.

has the car overheated?

the two codes together might not be a good thing, hopefully the engine head gasket is not bad.