Vehicle shudders at certain speeds and rpms.

Sounds like the torque converter. can be tricky, new one expensive, I had the same problem, talked to a buddy who is ford master mechanic, he told me to DRAIN, the TC, then put new fluid in. He said DRAIN, and NOT flush. because if you flush, and the magnet inside is missing or screwed up, it will push all of the little pieces of metal and **** into transmission. I had the dealership do this, and it cost around 150-200. It worked, and I was lucky, cause they told me it hadad no magnet, but it worked, not shuddered since.
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BroncoBobby