Suspension and shocks

Hey guys, I'm new here but I just finished a unique project of putting a '02 LS1 into a 2000 S10 extended cab Xtreme truck. Pulled the old 4.3L V6 out and put the LS1 in with an automatic transmission. Made it look as close to factory as I could. Now, I just noticed my cv joints going out on my driveshaft so I decided i needed to get that fixed as fast as i could. I hate two piece driveshafts (there are uses I know) so I found a dealer that sold one piece driveshafts for extended cab S10's. Its is a one piece aluminum 4" diameter driveshaft and it fits in there really good. If your familiar with the S10's two piece driveshafts there is a crossmember that holds a carrier bearing for the driveshaft. Right above that there is a lip on the bottom of the cab that I noticed after putting in the new driveshaft I didn't have much clearance because I have the Xtreme version and its lowered more than stock. So I did some notching and got that cut out for clearance. Then I went and tested and everything seemed fine. My LS1 has headers and an exhaust along with a good tune so its putting down good numbers around the 330 range to the wheels. When I do a wide open throttle pull from a dead stop, the rear end squats and the driveshaft probably flexes a little and it smacks the bottom of my cab at another spot other than the one I notched. I can't notch this one because there isn't a way to do it. So i'm looking at either a stiffer suspension setup in the back to prevent the squatting, maybe ladder bars might help, or something to prevent so much flexing. hope you guys can shed some light and help me out. Thanks.