My one and only experience with Jiffy Lube was finding the lock on the transmission dip stick bent out of the way after my daughter took our 745 there. We also bought a used 745 that had been to another Jiffy Lube regularly - it had a bent dipstick lock also!

When I discussed this with the manager, he apologized and said that their people were not trained to do this, but he never denied that they bent it!

As for high test, I strongly recommend it. Your premise that the knock sensor will take care of octane assumes that the sensor works. Older engines have carbon on the pistons, possibly making matters worse.

Also, I don't know about other cars, but I have read in a shop manual that the first action that occurs when the sensor acts up is a richening of the muxture, then the timing is adjusted. This is because the extra fuel can stop the knock and cool the cylinder at the same time and is faster than changing the timing.

I keep track of every gallon of fuel that I buy, and have seen a loss of 3-4 mpg on a trip using regular by accident.

Engine braking can be useful and fun. but unless you do it properly, you can subject the drive train to forces greater than the power that the engine can produce.

I think that an automatic transmission is suited to the characteristics of a turbo engine.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks