Hope taller tires won't hurt pinion angle too much

We probably need to see some videos of your launches, that would go a long way to be able to see the car in action. Gregsdart has the correct idea about a little softer launches too. If you haven't done it already, you might want to get the car up on cribbing so it sits at ride height and do some triangulation measurements. You may have the rear axle not square and true on the chassis, the frame rails may be tweaked a bit, or any of a number of other things. My former partner and I ran a Super Gas car and never understood why the car was so violent. We were told to check triangulation, and sure enough the rear axle was not true and square to the chassis. We corrected the problem and the car was a dream to race afterwards. Mine is just an example, you may want to experiment with rear tire pressures also. We used to go to some sketchy tracks for T&T before National or Divisional races, just to see if we could make the car launch correctly. I had another friend who broke a tie rod end on a launch and claimed that he only "brushed the wall". I went over and we triangulated the car and found out that he had wrinkled to left side subframe. It wasn't obvious until to got under the car. He had a body shop sponsor and took it to them and the wrinkle caused the right side of the car to 1/2" out of square. We don't know the history of your car, so we can only speculate as to what may, or may not be the problem. Good luck sorting the car out, I know it can be a PITA.