Thats usually one of the first mods people do on their L67 cars.

Intake > Exhaust > Pulley

As far as I have heard - there are no downsides to this mod. It was just that GM was being conservative to preserve tranny life, is all.

Keep in mind that 3.4" pulley will prolley set off bells if you try to take the car in for warranty work. The pulley caliper test is the first thing most GM dealers do nowadays on L67 cars.

So if you still have a warranty ... keep that in mind.