I suspect it needs more caster, it probably had 2 degree shims in it when new, 4 degree should help. Just watch out for thick shims or short center pins on the leaf springs, the center pin needs to pass through the shim and still locate in the axle center hole. I have seen some shims with a center hole and pin combination so the length of the spring pin is not a concern.
If the steering feels loose, or easy to turn, then it needs more caster. More caster is like adding weight to the front. You can tell a vehicle has a lot of caster when the front end rises and drops when going from full stop to stop with the steering wheel. With no or very little caster, the vehicle will stay level with the stop to stop turn test.
Joe
