Two pumps from THD, a 12 and 15 psi. My friend put the 15 on his and his truck pulls STAUNCHLY harder on the top, as well as improved throttle response. Once the hair dryer lights, truck still pulls hard instead of falling on its face like it did with the stock lift pump.
I noticed an awesome increase in throttle response, slightly harder pull on the top (I only have like 30 hp over stock, so that's why the "felt difference" was not as drastic). The biggest difference which I really felt, was the truck keeps pulling after the turbo lights. Same as my friends, before the THD pump the truck would start nosing over right after the charger spooled.
I know few people on here are still running the factory lift pump, but for anyone out there that needs fuel to the IP, get the pump and don't look back.