I think your 01 AWD is in the range Lexus specifies. Although you should do better with 89, what is your driving style?
I installed K&N drop in air filter, removed unneeded weight for daily commune, (spare tire, jack, and wrenches from the trunk). Also I thermo wraped my exhaust header and pipes a while ago. Not to spark a debate on merits of doing these mods but combined I am getting >24 mpg on HWY and >20 mpg mixed driving with 87 octane gas.
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Looks like the climate has a big factor in it. I used to get 23 during October when temperature is in the 60s. Now I only get 20 while temperature is 30s. That is why I saw guys from CA are reporting better results.
I am using KN drop-in air filter too.