I think there are some sound clips on the Ford Trucks Enthusiasts forums in the gasser forum. Might try the Diesel Stop also. I hear that changing the y pipe might make a fluttering sound at certain rpm's also. Ford necked the y pipe down to remedy the flutter complaints.
I have a v 10 also and got the Banks ottomind chip for free and didn't notice any improvement or decrease in performance or mileage. I have a stock exhaust but might do the muffler change. I think most like the aero chamber or 3 chamber flowmaster.