They do know their 4.6 engines though. But anyone that i know that got a chip done by them, had to go back at least once.
When my buddy does 4.6 cars, because of the lack of a dyno at his shop, he has jdm do chips. Too bad as i said, they all go back once or so. He also does the work itself fairly cheaper than jdm.
i had my car dyno tuned at there shop. they use SCT chips, i have a two tune chip with a switch one for the track(race gas) and one for the street. I had it done about 6 months ago and no problems so far.
They are a very busy shop and Jim seems to know his ****. Yes they are very expensive but i learned that you get what you pay for. I used to have a Diablo chip and i had two shops modify the chip for cheap but to do it right you need to run the car on a dyno while you are tuning it and JDM can do that. I would recommend spending the extra cash and having them do you work. However expect to be put on the schedule and wait ATLEAST a month for your appointment.
after their tune i shaved about half a second off the car to get me into the low 12's.......so far