As mentioned by others, check the SWR, and connections. The ground connection is the most important. Also inspect the antenna and connections for corrosion etc. If you know a local Amateur Radio Operator, they might have an SWR meter.
That is the best way to improve CB output. I would not add an amplifier, like truckers do.
That is the best way to improve CB output. I would not add an amplifier, like truckers do.