Cooling an auto transmission

This is a question for anyone who has installed an auto transmission in their Oka. What type/size/brand of transmission cooler do you use, and does it work effectively?
I currently have 2 large (250mm x 250mm) tube and fin coolers in series, which are not really up to the job on long hills. Our transmission is a 4l80e behind a 6BT engine. I am considering either a large stacked plate cooler or a water to oil heat exchanger plumbed into the return hose from the radiator. Has anyone had experience with these setups?
cheers
Tony

With the Allison heat is not a problem on hills unless you are going slow in second because of the lockup. It’s probably hard to compare a cooler for the two because of the higher pressure the Allison runs. I’ll Look in the morning. My cooler was supplied by heavy automatics. I have no problems with cooling even in the high heat up north with a load. Mine is mounted facing the rear tail shaft so I have a cover over the core that only has a 20mm gap to let air in so i’m mostly relying on the fan to move air through it. On a hot day the fan comes on at 93c and turns of at about 75c this might happen about every 25 min in 38c. If it’s below 30 it rarely comes on.

When I initially fitted the 4L80E behind the Perky I had 5/16 hard lines along the RH chassis rail to two tube and fin coolers in series mounted behind the front skid plate. The plate had the whole centre except for about 50mm around the edges cut out and replaced with mesh. the two coolers filled the whole area and had individual fans controlled by a Davies Craig fan controller.
In ambient air temps of over 25C the fans ran virtually continuously if the torque converter was unlocked.
In an attempt to increase fluid capacity and flow on the advice of a auto trans bloke I upped the lines to 1/2" which made a noticeable difference along with a fluid change to full synthetic, while this helped greatly it didn't stop the problem on long hills so in summer you had to drive by the trans temp gauge in hilly terrain with the torque converter unlocked.
I then changed the settings in the Compushift to allow torque converter lockup at up to 80% throttle which kept the torque converter locked for all except the biggest hills but as it was unlocked less it was cooler to start with.
The torque converter clutch lasted about 40k before it let go, one minute we happily cruising at 95 on the freeway the next the trans was cooked, took all of 30 seconds! The problem is that when the clutch material comes off it goes out through the coolers and back into the trans where it feeds the rear of the trans around the output shaft before going back into the pan to start the cycle again. Where it feeds around the rear shaft it goes through a banjo type fitting which has small holes and the clutch material from the torque converter just blocked them straight away, NO oil flow through the trans means a cooked trans pronto! I've said this a few times over the years, you MUST run a Magnefine inline filter on the cooler return line before the trans or you will cook it if the torque converter clutch lets go.
My trans and torque converter were brand new Heavy Duty Hummer H1 variants and the heaviest factory spec the trans was built from the factory I'm told. When the torque converter and trans were rebuilt I had the same problem a couple of years and about another 40k later but the second time because of the inline filter the torque converter clutch just started slipping and caused no damage to the trans.
So despite these experiences I then fitted a 6bt and all went swimmingly as it had a heap more grunt and could howl up hills in 4th with the toque converter locked, problem was I soon found out the extra grunt was too much for the torque converter and the clutch only lasted 5k after the 6bt went in so the torque converter was rebuilt again with a super dooper clutch lining etc etc and away we went. all went well until one day I lost drive completely as all the fluid had been pumped out which in turn cooked the trans. When I pulled it out I found the stem on the torque converter had cracked which promptly pumped all the fluid out on the road, no worries the torque converter man said we can beef it up and he did and it was fine until one fateful day many hundreds of kilometres from anywhere in the NW corner of the Great Victoria Desert it broke the torque converter stem yet again resulting in a 200km flat tow and a 1500 km ride on a tilt tray.
That was when I decided to listen to the trans blokes and accepted that a 5 - 6 tonne truck with a Cummins 6bt was way too much for what is a heavy duty car transmission. I know they can take a 1000hp but is only for short periods and they aren't trying to do it with the best part of 6 tonne on the back.
So I fitted a 6 speed Allison which I should have done in the first place, it certainly would have been cheaper and I might have more hair!
As Rob said the Allison torque converter is locked most of the time even under full throttle in every gear except 1st which stops any slip which is what heats fluid but it still doesn't heat the fluid up like a 4L80E even when going up big hills in low gears. Where a 4L80E runs about 30 psi pressure the Allison runs about 150psi which means full hydraulic hoses 5/8 ID and a fin and plate cooler. The cooler I run behind the modified bashplate is a Setrab about 300 x 400 with one fan and it is more than adequate. As Rob said the fan rarely comes on and long descents in cooler conditions the trans temp drops right back. It is rare for trans temps to get past 75 even on very hot days, I think I've seen 100 once on a 40 degree day climbing a very long hill in the high country. The Allison also runs full synthetic Allison Transynd fluid at $300 a 20l drum. at the right price, normal retail in Oz is about $450!

Thanks guys for all the advice and info. I can see Peter that you have had great trials and tribulations over your 4L80e. The Allison sounds like the best option, but a bit beyond my current budget. I will upgrade the cooling system, and treat the transmission with care, not push it too hard and keep my fingers crossed!