Where should I look for a short?

The place to start is by having the stored diagnostic fault code(s) read. The dealer and most transmission specialty shops have scanners that can access the Transmission Computer. Typically, if there's a problem with a sensor, the system will go to limp mode as soon as you shift into drive or start to move. If it goes to limp mode during or right after an up-shift, clutch pack slippage is more likely the cause. The Chrysler DRB3 scanner can also read out the clutch volume index, (CVI). That's a set of four numbers that correspond to the volume of fluid it takes to apply each clutch pack. An experienced transmission specialist can tell how much life is left in each clutch by those numbers.