Sea level air pressure is close to 100 kPa and that's what your 99 (kph?) with engine off is indicating. That is also equivalent to 29.9 in Hg and 14.7 psi. Anything less than that is usually referred to as a vacuum. To calculate manifold vacuum, subtract MAP sensor reading (in kPa) from 100. With a MAP of high 30s, the vacuum is in low 60s at idle. That vacuum would be about 18.5 inches which is about what it should be at idle.
When driving, the MAP reading will correspond fairly closely to the load being placed on the engine. When accelerating hard, accelerator pedal on the floor, the MAP sensor reading will go up close to 100, corresponding to a manifold vacuum close to zero. If you are moving at a moderate speed and get off the accelerator pedal (load on the engine gets smaller than when idling), and the MAP reading goes down to the low 30s and even the 20s). As the vehicle speed increases, there will generally be a greater engine load, and that will produce higher MAP readings.
But, you can't really predict exactly what the MAP readings should be in various phases of driving of a particular vehicle; you have to measure it. However, using your readings, I would say that the MAP sensor is not the cause of your misfires.
2001 WJ Limited with Quadra-Drive, Kenne Bell Supercharger, 3-inch Kolak exhaust, Stillen rotors (F/R) and MM pads, Addco sway bars (F/R).