I'm guessing mine is a bit of both it shakes before 55mph for me. but my angle isn't the best with my lift. I was thinking about finding a TJ front drive shaft with the double cardan joint
you would have to adjust the pinion angle if that is the issue, going to a cv joint at the t-case won't change that (for what is worth would be slightly more since you'd be pushing the outer CV u-joint forward) that also involves realigning the Cs on the axle to regain the caster angle (and not get the wobble issue) - TJ drivesaft would def help since it's balanced so that might solve your problem (i have no idea if it's CV or not but they are balanced since the pass axle is one piece).