Here's more info from my build thread: FJ60 5.7l TBI to 5.3l LS Swap - https://forum.ih8mud.com/threads/fj60-5-7l-tbi-to-5-3l-ls-swap.1000636/post-11194609
My LS swapped FJ60 never hits 200F in the 95F summer, in traffic, with the AC blasting. I do have an aluminum Champion radiator and an...
I'm curious about your heat issues. Do you have an H-pipe or tee within your heater circuit off the water pump? So that the in and out of the water pump are looped together even when your heater core is shut off?