Actually, 4G is barely deployed today. Most people get 4G LTE, which is somewhere between 3G and true 4G.You have to remember that they start work on a new vehicle 5-10 years before it goes on sale. So for Jeep think perhaps around 2008 or earlier they started working on it. 4G didn't come out really until 2012.
T-Mobile put up a true 4G tower near my home in AZ. I can get 100Mbs consistently - but only in one small spot in my front yard! I need a T-Mobile booster to get 4G-anything in my back yard. 5G is far worse in terms of spotty coverage and has a LONG way to go to be useful, IMO.
On a cross-country trip this year we saw just how spotty T-Mobile's "nationwide coverage" is. It largely depends on the capabilities of your particular phone. My wife's phone doesn't support the 600mhz band, but that's the technology in many of the new rural antennas T-Mobile is using.
5G is going to be similar. The Big Three are all using mmwave 5G bands but few devices can use it. Worse yet, the higher the frequency the spottier the coverage. I suspect that for quite some time in the future 5G data rates are going to vary a lot as one travels with frequent drop-back to 4G (or 4G LTE) speeds.
I wish cell phone companies would try to get the current technology somewhat perfected before moving on to the next. I suppose that's just modern life.