Does anyone know what would make shut down after it warms up?

Possible faulty Idle Air Control valve? Have scanned(live data , not 'code reader') and monitor IACs response to verify BEFORE wasting money on a guess.

maybe you have an ignition problem

A very common problem in Rams. Iradic low idle/ stalling. (1.) The Idle Air Control valve attemps to control idle speed by opening a port in the throttle valve assmbly. on top. This often gets dirty where the IAC pintal seats. Search procedure online for cleaning or just try throttle body spray,(not carb. cleaner) on top/rear of Thrt.Body and inside rear wide open TB. (2.) There is the Air Charge Temp. Sensor screwed into the top/right side/front intake manifold just under intake hose for the air filter housing. It sends signals to computer and affects control of IAC by comptr. Remove with wrench and spray cleaner down inside SENSOR or replace/install, about $29.00 @Adv Auto,. Replc. filter housing gasket and housing. Check elect. connections to IAC, TB positioner valve, ACI sensor. Good Luck