I have a Atlantic British 4.6 in mine with top-hat sleeves- my old 4.6 slipped a sleeve- it's definitely has more power then the old 4.6- but I still have all the other known potential problems with the motor and my local shop that installed it is telling me AB isn't honoring the warranties on the motors reliably. I already had to do head gaskets at 20k miles- my shop did it under warranty but they were not happy about it and said since AB didn't honor the warranty they wouldn't do it in the future. Also- there is still the oil pump problems etc. I spent $11k on this motor- for nearly no power increase and the only more reliable issue is it won't slip a sleeve now with the top-hats in there- but otherwise it was a colossal waste- but in my defense- the LS swap kits (ACE and such) came out two years afterward. I'm very, very much considering the ACE swap anyway with a good 5.3 from the scrap-yard- then when the trans goes out adding the 6l80 and it's 5 speeds into a Marks 4x4 adapt and going all the way with it. I'd STILL spend less then I did just on the AB long block. Anyone want a built 4.6 with a HP cam and $23k miles???