The air inlet door will very often stay open regardless of what the button is commanding due to a strategy built into the system in order to get fresh air into the cabin. Not sure if this is what you were experiencing at the time, but it’s normal.
The time interval they have listed doesn’t...
Any dealer can order them, regardless if you own a Stroppe or not.
But yes, you would need to change the fenders also if you have a normal bronco.
Unless you have a heritage, which the OP looks to have. Those use the same fenders as the Stroppe. So these flares would fit without any changes.
If you want power, the best way is a custom tune. None of the piggyback tunes or even the FP tune will come close to a custom tune.
Mine has been tuned by @ZFGracing for years now. Makes a ton of power, never had a single issue and runs flawlessly. They have a lot of different options for...
I know you said no check engine light, but did the dealer check for, or note any historical codes?
Doesn’t sound like phasers at all, more like potentially a throttle control issue if it was still running. Although that would typically set a check engine light right away.