Nice looking work! I'm not an engineer but a long time player in learning the hard way and playing with several hundred different set ups to see what works, what doesn't and why they do or don't. Also been chasing this knowledge for years before I ever saw a suspension calculator, I still don't use it while I'm building, I use it when I'm done because the owner usually wants to see it. The triangulation is sufficient, you have more than the average monster truck that is heavier and abused harder than anything you are going to do. Triangulation is not helping but not the biggest cause of the handling issues you are struggling with. The geometry of the links in the relationship to the ground are the biggest culprits. I have some basic rules that always work without fail. At ride height the upper control arm needs to be as close to parallel to the ground as possible to pointing down toward the front. The lowers need to be mounted with the frame end 35-50% of the vertical separation at the axle, depending on how much anti squat you want. For a 4 link I try to get 20% of the tire size for vertical separation at the axle, more if available, packaging always creates compromises to everything but usually can be worked to a compromise that functions well. Packaging permitting I make all of the control arms the same length, but will shorten the uppers up to 33% shorter than the lowers if necessary but still follow the same basic rules.
here's a sample of what the calculator looks like on my personal bronco. Please keep in mind I do not have a bronco frame, I built a rectangular tube frame that helped to accommodate this geometry, but have managed to get close on bronco's.