I'd take a good gander at the rear trailing arm bushings- I believe you said the were not replaced??
if the inner were wore out, it may cause your issue. or if someone put eccentrics in there incorrectly.

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.