My thoughts...
Oil (either trans or engine) needs to be at the RIGHT temperature. Drivers too often think that cooler is better, but that is not the case. Trans fluid is hydraulic fluid as well as lubricant. The whole transmission is designed to operate best in a certain range of temps. Too hot and things burn. Too cool and the thicker properties of the fluid can't properly operate the hydraulics as they were designed.
Engine oil is the same way. Too cool and it can't flow into the gaps like it should and you aren't lubing properly. If you go way too cool, you risk spiking oil pressure and opening the bypass valve which means you're not filtering. It also wants to be hot enough to evaporate/burn off things like blowby hydrocarbons and condensation. Of course, too hot has drawbacks as well. Oil too thin to properly suspend bearings, lower pressure, and cooking additives and hydrocarbons.
The benefit to having a radiator circuit for the transmission is that it helps get the transmission up to temperature as much as it sheds heat from the transmission. People fight me on this a lot, but I get so irked at people who insist on going crazy with cooling. Drivers like cool. Engines like hot.
I will also say that transmissions don't like complexity. An inline thermostat is a big no-no, especially for some transmissions. Many transmissions (including the one in your K truck) rely on the cooling circuit as part of the lubrication circuit. Simply stopping the flow of fluid can fry that trans in short order. You might be thinking a bypass stat would be better, but it's just an extra failure point waiting to happen. Unless you install a trans temp gauge and monitor it religiously to make sure the temps don't spike (stuck closed) or never get warm enough (stuck open), just skip it.
The real answer here is to get a radiator with a circuit for the trans. If you want additional cooling (and by that I mean only if you NEED additional cooling), then install a secondary cooler. Put it in front of the radiator, oversize it, then send it back through the radiator circuit. Don't fight me on this, I'm right. This has all kinds of benefits. If you just randomly send all the fluid through an external cooler, you have no control over the fluid temps. Did you oversize and it's too cool? Did you undersize it and it's too hot? Not to mention, it will be vastly different temps if you're stop and go, highway, towing, etc. Putting the extra trans cooler FIRST means that you can't oversize it. Let's say you're sending 230 degree fluid from the trans. If you send it through the radiator first, then the external, you are dropping the temps to 200 in the radiator, then randomly dropping them to whatever bulk heat gets shed in the external and sending back a big question mark to the transmission. If you do the external first, you can drop it to whatever you want... 180 maybe? Then sending it back through the radiator will bring it back up to the proper temperature. (and draw some heat out of the coolant as well instead of adding). Always put the known entity last in the circuit... in this case the radiator circuit.
For oil cooling, I would verify that you need it first. Randomly adding cooling can be a bad thing. Install a gauge, hitch a trailer to it, wait for a 90 degree day, and go climb a mountain with your foot to the floor. If the oil temps don't get over 230, you don't need an oil cooler. If they don't get over 250 for synthetic, you don't need an oil cooler. The oil in an engine spends a considerable amount of time on the other side of water jackets. and is pretty good at cooling itself. Ford 460, not so much. B and RB mopars, not so much. Chevys... pretty good.