I've done electronics all my life - use to make mobile/base illegal CB amplifiers back in the 70s during the heyday of CB (have the required high voltage scars) and crazy enough to be installer for large antennas 100+ foot towers ( I believe they still make Moonraker antennas), later went legit with amateur radio... besides the usual home brew rigs helped with a 1KW mobile install - the arcs we could draw off the antenna were really something - RF tubes were great stuff - wish RF electronics surplus was still widely available and cheap.
With grounded antennas on a Jeep, I think seeing SWR ratio's 2 to 3 and above indicates a serious problem.
First thing I would do is check the coax isn't shorted (registering anything on an Ohm meter) - especially if I cut the cable and put on my own connector - it is easy to get a small strand of shield that you can barely see shorting the connector. Also take a reading along the length to make sure there is good contact (i.e. very low ohm reading).
Stay away from groundless antennas - too quirky and no reason to do that on a metal Jeep - leave those for fiberglass boats. Have to have a good ground to the chassis, sandpaper paint away for any bolt/washer/nut. Don't get those "cut to tune" antennas - easy too snip too much and then it is a throw away.
I have a tunable slug antenna from Radio Shack - SWR 1.0 to 1.1 across the CB band (tune on a center channel or if you use only one channel pick that one to tune the SWR on). I cut the coax to length with my own soldered connectors.
I agree with the coax length not being very relevant for grounded antennas - just don't round coil up extra length.
Oh - one last thing, make sure you understand how to set up your SWR meter - read the instructions!
I use the CB on the Jeep for communication in groups. CB does not transmit very far mounted on a Jeep - better to get an amateur license (which is not difficult these days) if you want a radio for emergencies in the outback.