I had the same issue and was pissed after driving 300 miles and put in in 4WD to find out I had a problem!!!

I have successfully installed a 6" Stage 2 ProComp lift and had the exhaust/drive shaft issue. At first, the drive shaft rubbed the cat and then we took it back. I had a heavy-duty adjustable front track bar installed in addition to the lift components. (Since they didn't catch it, they gave me the $350 track bar for free!!!) Before and after installation, we took measurements of the front-end geometry and the track bar even straightened up the tracking better than with just the ProComp lift components. I now have approximately 1/2 to 1 inch clearance between the cat and drive shaft. I suggested they contact ProComp, but everyone knows how that ended up. I have had zero issues since and 20,000 miles, and daily off-roading with lots of flex.

FWIW - I am running the above lift, 37x12.5x18 tires on 18x9 rims.

Hope this helps.