There are common issues between Jen Juan and Jen Too. very softly sprung, leaf spring rear suspension. Your truck is amplifying the problem even past Jen Too levels - remember stock Jen Too torque is way higher than stock Jen Juan.
@FordTechOne is right - the TRX had a lot of investment spent in handling the kind of power -and weight of the truck, whereas you are modifying a platform designed for a naturally aspirated truck at 400+ crank HP. It’s way overwhelmed.
Best guess. You need slightly stiffer springs, traction bars and probably revalved shocks. The traction bars can go on right away, but, you need to decide if you’re going to lift the truck or not FIRST. IMO, what makes the Rap good is its low center of gravity for an off road truck.
Traction bars will do a few things.
1) pretty much eliminate axle hop.
2) eliminate axle wrap; the tendency of the axle to torque down, grab, twist the axle in one direction because of the force applied on one side, release, repeat.
3) positively locate the axle in a single plane as the suspension articulates.
Even with Deavers, your leafs and shocks are probably well overpowered.
I have a Jen Too, but it’s very, very easy to cause a LOT of rear suspension drama in the dirt or sand or even the street in 2hi. If you ever watched the chase scene in Bullitt, that’s a good demonstration of leaf spring suspension being overwhelmed. That’s what’s happening.
I looked hard at traction bars but went with the KHC torque arm. It’s a night and day difference. When I took off at full throttle before the T/A in 2Hi, it was a thumping, fishtailing, lack of control. the same launch on the same pavement and the same sand was completely different. On pavement there was at least a 95% reduction in steering wheel correction. The truck tracked straight and introduced no unexpected drama into the launch. In the sand I have a lot more predictability than before.
At least in theory, the traction bars should be superior in axle location. I think SVC and Rogue were making them.
good luck!