Need input on steering wheel shake - balance not the problem

Hi all,
I need your input and opinions. I have a 2010 Crewmax with 59,xxx miles on it. I had an alignment 6 months ago with 24" wheels/tires. I recently put on stock 2019 TRD 20" wheels and tires with less than 1500 miles on it. The original owner removed the TPMS but didn't rebalance. I put them on and at about 55 mph the steering wheel shakes pretty violently. I figured the tires were out of balance because of no TPMS, so I just got them balanced. Took them on the highway, and same shaking at the same speed; no improvement or change at all. I called Firestone (who did the balance) and they said the tires were balanced when put on. They said it could possibly be the alignment. With that being said, although I just got an alignment recently, could that be the need? Or could it be more? I've searched and read about other threads of the torque convertor, rear axle (?), etc. Any idea? Thanks in advance.