Again no guru here and different set up but this is my mates RR with 10x29's@17psi, 8" wheel, caltrac/mono's rear with calvert shocks on 7 tight, 20yr old 90/10's up front
, 3800lb car, mega block+11" drums and heavy street wheels/tyres, could be much better, some wasted motion there as well but not as bad as your truck when it tops out unloading rear, he's gone 1.42 60 best, and yes hit the tyre harder by moving the bars up and control the rebound with the shocks to keep tyre planted, tighten the front.
https://www.youtube.com/watch?v=9tnu9cSnf2U