If your temperature was still climbing while at speed out on a 4 lane highway the fan isn’t the issue. At highway speeds the clutch shouldn’t even be spinning the fan, so the shroud shouldn’t be the issue. The fan should be about 1” inside the shroud, but being a little off will only be a small efficiency change, not a drastic problem.
So if your temps are climbing at speed usually the issue is that the radiator is on the small side (or plugged up), or you may have a circulation problem. The smaller water pump pulley would speed up the fan (when it’s spinning), but it would also spin the pump faster too. Which may help with the sustained speed temps.
