Actually, range of communication with a CB, & just about anything else that transmits/receives via "radio waves" depends on a lot of variables. As far as a CB goes; most true CB radios come from the manufacturer set to transmit somewhere between 3 to 3.9 watts or so. As mandated by the FCC; the maximum amount of power (wattage) that can be used to transmit on the CB band (also known as the 27 Mhz band) is 4 watts.
That being said, your range will depend on how well your antenna is set up, how well the antenna base & bracket is bonded/grounded to the body & the rest of your jeep, the quality of coax you use (Good RG-58 or 8X is more than sufficient), & if your SWR is set correctly.
It will also depend on the terrain you are in as well, but you should be getting more than 3/4 of a mile out of your radio. It should be good for 2 - 3 miles at least, well, unless propagation "skip" is plentiful at the time. Also &/or you are down in a valley while wheeling through tall hills & mountainous terrain where the hills/mountains are very close together like in the hollers of Kentucky, Virginia, West Virginia, etc. etc.
The first thing I would do, is make sure your SWR is set correctly, & go from there.