Hayden Rapid Cool #1-7511. Its supposed to be for motor homes towing over 10K lbs. I bypassed and plugged the radiator tank cooler altogather after Auggie gave me a "heads-up" on several splitting the heatexchanger in the radiator tank and dumping coolant into the trans and frying the tranny. Mine is out of warranty and I don't want to buy/rebuild a trans if I don't have to.

So far my trans runs about 1/2 to 2/3 the previous temps @80+F ambient and hasn't exceeded its previous normal temps on the hardest pulls. Coolant temps now stay well below 210. Remains to be seen if it will be sufficient when the ambient temp hits 100F and 95%RH. Might be necessary to add another in series similar to your setup Phil.

Here is the best pic I could get without pulling the grill:

That pretty well sums it up Phil. I never noticed any better cooling in tow/haul only higher RPM shift points. It still kicks out of lockup and comes back on the converter under a hard pull.

"When I've towed, I've noticed that the TC rarely stays locked for long, even with tow/haul on. Does two/haul help lock it up at all, or simply play with the shift points, in which case I'm guessing that the tow/haul mode does little to help with cooling?"
Thanks PhilD, I thought that the TC locked up more in the Tow/Haul mode more...I did the same additional trans cooler per your post and it really works great. Thank you again!

I ran new lines from where the stock line entered the lower fitting on the rad tank to the cooler. Plugged fittings in rad tank to stop coolant leaking out if old tank cooler ever does split. The return line has a coupling close to this point, popped it loose and ran new line from cooler back to that point. BTW- the factory flare on the line makes a great hose barb. Did a similar flare on cut line to the cooler to create a similar hose barb.

Also while still on the subject, I question how much pressure is on those lines (need to do some further pressure checks). I noticed all hose moved back slightly until clamp/hose rested against the barbs with clamps tightened properly. Had I not done the barb/flare thing the line would most likely blew off. Something might be going on here with the pressures and be the underlying cause of the stock tank coolers to split/rupture (shouldn't be that much pressure).

I questioned why only trans cooler splits and not eng. oil cooler. It seems over 1800 T-coolers have been reported under warranty and only 2 known eng. oil cooler failures warrantied. They both are very similar in construction I believe.

Well i have to say, this thread provided a wealth of information......thanks all for the input. keep it coming.