You may have fouled out that 02 sensor if it has been way rich the entire 75 miles + idling. Would dropping the pressure to about 34-38 lbs. help?
We are putting dual EZ throttle bodies on a 426 Hemi and the tech at FAST said to start at 32lbs.

Brad


Check out the Dorn's 69 Barracuda "Switchblade" in the Nov.2010 MCG
Check out the Dorn's refurbished 36 Ford in the Feb.2011 Street Rodder