The cognito's will compress about the same as the OEM shock, so here is where your problem comes from. When you cranked the TBs, you raised the lower control arm off of the bump stop. The bump stop touching from the factory was what prevented nose dive and body roll and getting blown around from side winds.
When you cranked the TBs you reduced your downward suspension droop. Installing the longer cognito shocks will allow more droop. However, you are still faced with the problem of not touching the bump stops.
I am currently not aware of a way to extend the factory stop. The best thing you can do is to install the Cognitos. With the vehicle on a flat surface and sitting at ride height, stick a tape measure up inside the shock boot to measure how long the external space is on the shock rod.
Call up Daystar and ask if BLACK (stiff) bump stops:
http://www.daystarproducts.com/ItemF...09059&Category= will fit over the H3 type shock mount as it is not the same as the standard ordinary shock mount as shown in their video
Make sure and ask them the height to ensure they are at least as long (preferably slightly longer to allow for compression) as the space you measured above. If not long enough, get 2 sets and trim to hieght you need. Do not get their handy install device shown in the video as it will not work on the H3 shock mount.
The Daystar bump stops may however be able to slide over the body of the shock. Here is a pic to see how they are made:
http://cognitomotorsports.com/store/Hummer_H3.html