You asking him to explain his findings is perfectly ok! If I were you I'd contact Deysha here on the forum first before taking it in. She'll be able to escalate if necessary. Just send her a brief message with your issues along with your contact info, VIN# and mileage.
I too plan on bringing in my Stang tomorrow with similar issues. I have aftermarket parts as well and I must admit I'm a little nervous. I hope all everything works out for you. Good luck!