Let me try with a few suggestions that I did to my 95' LS, that was tired as well. This could save you a LOT of money and might scratch that itch.
First: go to the dealer and buy TWO gaskets for the throttle body housing. Then, find a buddy with a dremel, and hopefully a flex hose attachement. Then, buy a steel brissle wire bit for the dremmel. Now, take the intake off the throttle body "at which you'll see why you needed that new gasket. Take the dremmel with the wire brush, and clean the butterfly on the throttle body. In addition, this is where the flex hose attachment comes in handy, get inside of the intake and run the wire brush around in there to chew up the carbon build up. When you're done, do the best you can to clear out the loose debrie in the intake left from the dremel. If you can get your hand in there, then take a GOOD rag, and some SeaFoam, soak the rag, and wipe out the intake. Put it back together with the new gasket.
Next: learn how to seafoam the engine via the brake booster line. I'm sure if you search on here, or the internet, you'll find lots of info on how to do it "it's super easy".
Then, after you've seafoamed it, replace the plugs, and if your wires are original with that kind of mileage, I'd get new ones as well. Your call on OEM or not. You know OEM is the right path from the start, but aftermarket could offer some benefits as well "like to your wallet". Might want a new distributor cap as well.
When it's done, what you have accomplished is reestablishing the engine's breathing ability back to new. The seafoam in the intake via brake booster line, will help the valves big time.
When I did this to my LS, with 120k on clock, and 10 years under the belt, it brought that engine back to NEW. It was so powerful after this chore, that I barely had to touch the gas peddle to maintain cruising speed of 80 mph. And when the fall air hit, that cool clean air, that car was on fire with speed! It was awesome! Many older LS, GS, and IS owners do this around 100k, and none have reported anything but fantastic results. I'm a guru on the lexus forum, have been for years, and stand behind my opinion that any new owner of an older high mileage toyota engine should do this!
With most engines, but especially the fine engines from Toyota, four things determine the engine's performance: Air, Spark, Fuel, fluids. When one gets out of balance, you can tell. At 275k miles, I'm willing to bet the farm, that the breathing aspect is in need of some help. I'm wiling to bet spark has been addressed, otherwise you probably wouldn't be at those miles. Fuel has probably been addressed as well "fuel filter". But I doubt the intake has been properly cleaned. Give this a shot "total cost probably $30 at best" and post back. Also, make sure you've got a clean air filter too.
