Looks like the truck companies are fighting pretty hard over this... http://www.navistar.com/Navistar/EPA+2010/Advanced+EGR/EPA+2010
The order board for D6Ts is all Tier 4 now! Hope nobody waited to long!
I've read that the engin builders are all for the scr's because it lets them remove alot of the emision stuff from the motor. so the motor can run cooler and more efficently and let the scrubbers remove all the emisions after the fact. the only problem i find is the expence to fix something thats not a problem. but thats what goverment does. take something simple and complacate it.