Water temp varies too much. Perfectly, it should sit at exactly 92 C, that's the value I observe on most 1UZ's no matter if it's 1992 or say 1999 model.
You can run diagnostics on OBD1 LS400 with little effort, basically just a laptop with usb-rs232 converter and a couple wires
Fuel consumption wise, what voltages do you observe at VF1/VF2 terminals in the diag. connector? (when the engine is warm and running, check through all rev range). How many O2 sensors do you run, are there any cats? Do you have any error codes stored in ECU memory?