So far so good have 16k on the new engine and about 2k the tranny. The low and mid range on the beast is solid and I have only went WOT maybe 3x...it's fun for sure. The mileage really never changed still pretty crappy with the 408 I get around 10 to 11 in the city depending on throttle usage and about 14-16 on the highway once again depending on throttle...but then again I didn't build this with mpg in mind. When I pull my trailer I get around 8-10 on the highway going 65 to 70 mph in tow mode. I will tell you that I am looking at Forced Induction now as I (not my wife....) am used to the power. The good thing is everything is in place to either bolt on a supercharger or do a turbo kit....stay tuned!!
The 4L80 conversion what a pain in the ass like most of this custom build and took a bit longer to sort out but now it's bullet proof. Hope that answers the question