Since you don't have any information listed about your WJ, I'll split the difference on the weight. Feel free to recalculate if you need to adjust the weight estimations.
WJ Weight: 4200lbs
Max Load (for your listed tire): 2910
Max PSI (for your listed tire): 80
4200 + 400 = 4600 overall weight
4600 / 4 = 1150 lbs per tire
1150 x 1.15 (15% margin of error) = 1322.5 lbs per tire
1322.5 / 2910 = 0.454 (indicating you are using 45% of the tire's max weight)
0.454 x 80 = 36.357
Calculations show 36 psi is probably your ideal pressure to aim at. Another way to be sure is to chalk test the tire.