v10 excursion problems

[whiteexc22]

hey guys i need some help in a bad way...my excursion had been to 4 shops and has been sitting for 7 months now...when you drive the thing and pull up to a stop light or a stop sign and prepare to stop and when you do stop the motor lugs down to around 400 rpm and wants to stall and sometimes does and when you pull away it shifts down to first,so its like it stays in second while your on the break and when you let off the brake pedal and start to roll it shifts down...it also at an idle in park stalls and misses every once in a while...sounds like a machine gun sound at an idle....iac has been changed,,,maf has been changed,,,cops have been changed,,,,speed sensors have been changed.....check engine light is on but registering no codes? tranny shop ran the tranny for codes but came up with nothing....im at wits end trying to fig this out...could it be the main computer? i dunno whats left so hopefully someone out here can help

[BareBones]

How's the pressure in your fuel rail? And what happens if you shift to neutral when you're at 400 rpm? Check your air horn for a rat's nest....