If the temp is above 80 the a/c blows warm then cool then warm...no amount of fiddling fixes it. Have had a/c refrigerant changed and system leak fixed. What could it be?

 

Is that with "Auto" mode enabled? Could the temp sensor that controls "Auto" be going out? Or does it do the same with just A/C and a constant fan setting?

My A/C works great on my 01 LS 430. My one complaint is it is too cold. I have to set it to 74 or 75 if the temp is in the mid to upper 80s. Otherwise it is too cold in the car.

 

There is an option to adjust an offset to the set temperature at customization parameters:


Also I have the same kind of issue with my A/C that it works intermittently.
I will try this other customization parameter:

 

OK - I had same thing. And I ignored step 1. Pull off the cover and check the radiator and coolant reservoir. Mine was getting low. Filled it up and voila- everything works with AC just fine.

Before that I had changed the HVAC pressure switch and recharged the system. Mine was intermittent etc so the problem seemed more complicated than it was (electrical/switch/sensors).

Our cars are all getting to the point where hoses/rubber lines/radiator caps are all probably needing a refresh :-D

 

I do not know what mileage or year your LS is but i have an 04 and an 06. My 04 had an issue where it wouldn't cool off for the first few minutes of running first thing in the morning. The coolant level was full and the refrigerant was also full. What the issue ended up being was the AC compressor. These cars don't use a compressor with a magnetic clutch to activate it. Instead it has a solenoid that moves a plate creating a variable output. Toyota calls it a "swash plate." Using this style makes it so that the vehicle doesn't have the harsh kick on and off when the compressor cycles instead it varies the output causing a seamless transition.
What goes wrong is that if the plate rides in one place for an extended period of time it will wear a slight groove into the housing of the compressor. If the solenoid can't overcome the groove it can't vary the output.
Anyway, my 04 had this issue and replacing the compressor has fixed it. I am not suggesting this is what your issue is however it could be worth looking into.