Help engine problems!

check all the vacum lines. you may have one that`s off or cut or dryrotted causing a leak and making you lose power. Quaker State is great oil. they had problems in the 70`s with synthetic formulas but that was 30 years ago. castrol on the other hand does not have the best thermal protection like they claim. it is no better than other oils.

the best thing you can do is use a standard 5w30 oil and add a bottle of Lucas brand oil conditioner as your last quart in an oil change.
Lucas leaves a film of oil on all parts to prevent "dry starts" in the morning or after the car has sat for over a day not running. "dry starts" cause the most damage to an engine. i doubt your timing is off as it is controlled by the computer.

also check to make sure the oil breather hose is connected to the drivers side valve cover and the hose for it is connected to the rubber intake pipe between the filter box and T-body. if this is not hooked up in the right place the 3.8 wont run right. replace the pcv valve also. if it is stuck it can cause the engine to be a dog

use only 5w30 in the 3.8 it is designed for it 10w30 is too thick. it shouldn`t make much of a power difference but the engine is new and "tight" so the thinner 5w30 is better

As for the 100mph maximum speed... You might be hitting the computers spark cut. I know my 1996 V-6 cuts spark at 115 mph. The 1995 might be at 100. As for hesitation when you hit the gas. I can't help there.

I can tell you that you are seriously wasting money with the 93 oct and oct booster. Get back to reg 87 and ditch the booster. As far as plugs, I have always run Autolite coppers and never had a problem. If you want to change the wires, then I'd suggest just stock replacements. If you want some pretty colors under the hood, you could always go with Jacobs (blue) or MSD (red), but don't look for any performance gain, especially in stock or near-stock applications.