I have been at everything from 30 on down at 2-3 psi increments with terrible tire wear. Granted, if these were "regular" tires for any Jeep, 19 would be awefully low, but these are the stock "E" rated tires. They aren't even squatted at this pressure.
While it may be costing me gas milage, in real world dollars, how much? Not much, it is a brick in the wind. One or two mpg does not matter to me much. Better tire wear is a little more important for me.
At the higher pressures, it would not be any time at all and the tires would cup and the front part of the bars or blocks of the tread would wear worse than the back part of each bar. It would make driving a terrible experience and increase noise. Not bad when the top and doors are on, but summer driving with the top and doors off was a bit annoying.
While I am not an expert, I feel that with the "overkill" of a sizewall my stock tires have, 19-20 psi is not a terrible pressure to run at, especially given my personal driving habits.
A quote from my wife: "I don't even want to know how much it cost, I'm not in the mood to be that pissed off today."