Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the base station & the truck's CB radios. Additionally, please describe the power supply, the antenna and type of coaxial cable used for both.
Still, who has the trouble receiving; the base operator or the truckers please?
Offhand, possible / proposed preliminary tries (if have not been done) would be to improve/change antenna(s).