https://www.wranglerforum.com/f210/bump ... 281-2.html This thread is talking exactly what you are facing. Recent addition of the aftermarket bumper... and now has cooling issues on long pulls.
Takes off bumper, no problems.
Installs it again, problems return.
Seemed to be the general consensus that if everything is working as designed, (fan clutch, WP, thermostat, air flow over the radiator) then there probably isn't a bumper yet built to cause enough disturbance of airflow.. or at least enough to cause cooling issues.
His problem was not enough coolant in a non burped engine. The system, even w/0 enough coolant, apparently was 'ok' with the heat it needed to move with the amount of air flowing.
Add a 'change' of air flow, and he found out it wasn't adequate!
I'll ask you, when yours heats up, does it quickly cool down (say 10 seconds or less) or more like 5-10 minutes when you either level off on the road, or are just driving around at non-combat speeds? LOL