A bad brake booster will give you a hard pedal, not a soft one. You just will have to push really hard on the pedal to get it to stop. If your pedal is sinking it isn't the booster. If you didn't bench bleed the master cylinder, there's probably still lots of air in the system, some of it now pushed down into the lines. Your best bet would be first to loosen the connections on the MC and do an on-site bleed, then tighten them and bleed the entire system wheel by wheel. A drag indeed, but when you're done you'll not only have bled the system but flushed it, which is a good thing every once in a while anyway. A vacuum pump makes this job much easier. Open only one bleeder at a time, and always start at the brake that is farther from the master cylinder: right rear, left rear, right front, left front (unless your Jeep is a postal/British/Japanese one).
Test the booster by first pumping the pedal a few times with engine off to use any reserve of vacuum. Then, with foot firmly on pedal, start engine. If the pedal sinks, your booster is working. Let go of pedal, shut off engine. Now let it sit for a few hours. Go out and push pedal. If you still feel boost, and it takes a couple of pedal pushes before the pedal hardens up, the booster is both working and holding vacuum. A really bad booster might leak on your feet too, or send fluid into the engine, which will make big black exhaust clouds every time you stop. It might also hiss, whistle or stall the engine.