Low stall speed will cause higher temps at idle. The tighter the converter, the more it will raise the temp at idle.
The deleted heat exchanger is 90% of the problem. When you're not moving, the front cooler is almost useless. The reason the temp continues to rise is the pan temp rises because the deleted exchanger combined with not moving. Once the pan temp hits 200+, the outlet temp from a low stall converter hits 240+.
On my 98' daily driver, it has a temp probe on the hot line just like your truck. On the highway with the converter locked, temps run 100-130 in the winter time, 135-150 in the summer. When I pull up to a light or pull off the freeway, temp will quickly rise to 180 because the front cooler no longer does anything and the heat exchanger is holding the fluid temp in the pan equal with coolant temp at 180*. After a few minutes, tranny hot-line temp will get up to 190, and after about 10 minutes, it will peak out at 205*. Pan temp eventually gets up to coolant temp of 180-185 and then the converter is raising the temp the extra 20-25* to 205*. If I then put the tranny in neutral, it will drop to about 190* after about a minute, but it won't go below that level because the pan temp is dictated by the heat exchanger temp with is dictated by coolant temp. Dodge put the heat exchanger in there for a reason, and you just found out why.
A possible solution would be to put a second fan-driven cooler under the truck. If you don't want to spend $250, reinstall the factory heat exchanger. In my opinion, temp over 240*F needs to be addressed, otherwise the fluid will not last as long. On a play truck, not a big deal. On reliable transportation, the temp problem needs to be addressed.
One more example: My 95' street-legal race truck has a modified thermostat so coolant temp stays right at 140*F. In traffic at a light, tranny temp in the hot line will never exceed 170*F. Pan temp will never get over about 145* unless I'm hotlapping it at the race track. This tranny runs really high line pressure which adds a lot more heat to the fluid but I'm telling you from experience, the factory heat exchanger is incredibly efficient at removing heat from the tranny fluid.
