I've got a 4th gen with V8, but I'll chime in anyway. I find that when I'm in city driving, 40 mph or less for long periods, run one gear down, not in normal drive so trans doesn't shift into OD. On the V8 it seems that the HP requirement for OD is more than the increased rpm penalty as far as fuel economy is concerned. Not saying I see great advantage, but have noticed at least .2 mpg on the display.
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2003 Limited, V8, AWD. 4600 Bils/FJ springs, 1/2" spacer, SPC UCA, Super Pro bushings in front LCA and in all rear control arms, Michelin 265/65R17 LTX/Defenders, stock wheels with homemade center caps, Stop Tech slotted rotors w/Posi Quiet pads all around.
I drive 100% in Boston, we get awful millage, like 10-11MPG been like that for years. Its much better than my old 1996 LC80, that thing got on a good day 8-9MPG in the city on my commute.