Thanks for posting this link in the other radiator thread. I just did this this to mine and I have a few questions for you about temps if you would like to answer since our set ups and location seem to be so similar.
I went with the AN 6 adapter from Summit out of the trans and added a sending unit right there. I ordered new solid lines from amazon and modified them a little. I also picked up the Ridgid 37 degree flare tool to go from the stock solid lines to AN 6 with the nuts and bushings from Summit. Mine runs out of the trans to a spin on filter adapter I mounted to the cross member up front under the radiator that holds a filter the same as the engine oil filter. From there, I used aluminum hard line again from Summit to go to the bottom of the same Hayden cooler you have. Out the top with the aluminum hard line to the bottom of the factory trans cooler in the radiator (with a short hose between the two). I used the stock outlet line from the top of the radiator cooler and had it and the inlet modified by my favorite local hose shop. They brazed or soldered AN 6 adapters where I wanted them and then made all of the soft hoses with hydraulic type fittings to tie it all together.
At the time I did this, I replaced the radiator with a new stock style, water pump(gates), cap, thermostat and all the coolant hoses. I was able to flush the block with a steam cleaner and flushed the heater core as well. I also replaced the fan clutch with the ZJ one from Napa.
All of that out of the way, it seems to run hot in town. Stop and go when its 100 or better outside keeps both temps around 220 or better. I haven't wheeled it yet but I imagine the condition will be worse when crawling along. It will also overheat when idling for extended periods in gear or not. When it is warm, the engine and trans run about the same temp. The highway is a completely different story. The trans takes a long time to warm up and runs way cooler (150 to 160, 170 if ambient is over 100) than the engine, which stays on the thermostat (185 or so). The highway condition was anticipated and is why I used the factory trans cooler in addition to the external. The idea being to put some water heat in the atf to keep it from being too cool at high speeds. I was hoping for some additional heat exchange the other way at low speeds though (the ATF taking some water heat). Now being that the stock and aftermarket trans coolers are of different size and efficiency, I had no idea what to expect but the results are much less than desired. I was really hoping for consistency and slightly better cooling more than anything.
I'm just guessing here that the increased hot air flow from the trans cooler coming across the radiator with the more robust ZJ fan clutch is aggravating the stop and go and Idle condition. My air conditioner seems to be oblivious though. Until I get to the high of the highs, it still blows ice cold as it always has and is the requirement for our area.
Now I'm leaning towards a "better" radiator. I have avoided one thus far because of the interwebs horror stories and a little prior experience with a Dodge pickup that got hotter and hotter as the radiators got bigger and aluminumer.
Are you experiencing the desired consistent cool temps or do you have wild fluctuations like me?