I can't claim to be a expert but the only way I know to allow TC lockup is
by using the TCC solenoid. A very simple way to control lockup is by running
+v through your brake switch and then into the 4 prong connector in your
tranny. You don't need any ECM input this way but you still have 1 wire
going to the plug.All other switches such as temp and downshift switches are
available as case grounded single prong switches that are wired in series
with the TCC solenoid. You have to have your brake switch in series to
prevent the TC from being locked while you have the brake on, would be like
braking a standard with the clutch engaged. It is common practice to disable
the TCC solenoid and replace the TC with one designed for a nonlockup 700,
basically making it a THM 400. If you have nothing plugged into the 4 wire
connector on the drivers side of the case, just above the pan, I doubt you
have any TC lockup. At least I don't know how to make it work like that. If
anyone else does please let me know. I would guess that it is very unlikely
for your in radiator cooler to transfer enough heat from the tranny to
overheat the vehicle. If the tranny was getting that hot you would have
surely fried it by now. There is a line pressure check port directly above
where the shift linkage enters the case. I believe it is 1/4 npt. This is a
check port for diagnosing the tranny, very helpful to use a  pressure guage
with a long hose and watch it during driving. You can also screw in a temp
sender here to check your tranny temp

Mine never overheated.  One failure was blamed on a defective (and too
small) TConverter.  Apparantly there's two models which are different
diameters and have different bolt holes in the flex plate.  I installed
everything myself and can vouch for the fact that the only hookup is with
the throttle cable which has some very fine adjustment positions (for shift
points).  I seem to recall that I was told the shifting is controlled only
by the valve body and pressure in this modification.  I definitely have 4
"gears".  The TC locks up around 40mph.  I was told that a "little" off on
the throttle cable adjustment can cause slippage (and maybe overheating).
LD

As I understand it, there is a position that is optimal.  A click in or out
from this point is still OK and WILL change the shift points.  Too much
deviation from the optimal can damage the transmission.  As I recall, the
"starting point is to adjust tight and maybe with some help, mash the pedal
to the floor, causing the adjustment to "slip" into the correct position.
this may work only with the modified valve body for the non-electric shift.
LD