Bring some life back into her by changing ALL the ignition coils, plugs, cam sensor, o2 sensors - new cat, air filter, repack your bearings and you should gain back some mpg.
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For why? I mean, the coils don't wear down like old points or cap and rotor. Neither do the cam sensors. They either work or the don't. Sure, sometimes they work intermittently, but that counts as not working in my book. O2 sensors are typically the same; with the engine monitoring on this truck, it should be be able to sniff out a faulty O2 sensor (and throw a corresponding code). Otherwise, it's still working. The plugs - sure, change 'em. But he's done that. Air filter - WOW - 100k on a filter?? I make it maybe 20-25k, but it is fairly dusty around here in the warmer months. As for cats, that's a mixed bag. A clogged one usually presents other symptoms, too, but you're welcome to pull one off and have a gander. No sense in spending $1k on stuff you don't need to do. As for bearings, there really aren't any serviceable bearings to repack on the tundra.
I would, however, recommend a fluid exchange on the entire drivetrain - front and rear diffs, transfer case, and transmission. The diffs and t case all take the same gear oil; get a high quality synthetic 75w90. I like Mobil1, personally. They all have drain plugs, so loosen the FILL PLUG FIRST (to make sure you can fill it back up) then drain them and fill them. Simple. Use the factory WS transmission fluid for the trans and either do a couple of drain/refill intervals with the pan drain plug or use the bucket method and a helper to continuously drain and top off the trans while the trans pumps the fluid through the system. I believe there is also a serviceable filter in the trans that you can access by dropping the pan. I haven't done it yet, but may do it here shortly.
I'm sure everybody has their own thoughts on whether or not to drain and fill a high mileage transmission. Personally, I've never had a high mileage trans take a dump from a fluid exchange. I even changed the fluid and filter for a friend with a high mileage (almost 200k) 4l60e that was acting up (not slipping, but very slow to decide on gear selection and sluggish) and it drove like new for another 50k til he sold it. I've purchased several vehicles with bad transmissions because the fluid was never changed, but never a bad one from somebody who just changed the fluid and the vehicle died. But if the trans is already on it's way out - well that's another story. But your aren't going to hurt it by putting clean fluid back in to it.
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Blenton = Mike Sweers