4.0 shudders in reverse

Hi all, got and issue with my 95 ZJ. Next month it’ll turn 300k miles and lately its been acting up. So I replaced the spark plugs, wires and new cap and rotor. Runs much better than before the issue but the engine still shudders when in reverse when hot. when engine is cold, reverse is normal. I also replaced the front exhaust pipe but kept the old O2S/ oxygen sensor and put it on the front exhaust pipe. Now its throwing me codes 21 and 51. looks like the oxygen sensor is at fault? but is that why it still shutters in reverse when engine is at normal operating temperature. Maybe a cracked new distributor cap? timing belt? fuel filter? any and all help would be nice. Thanks guys

I’m going to say the shuddering is a transmission issue.

The shuddering I should say is more like a rough idle.

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