Truck jerks at high speeds when let off the gas randomly?

My truck runs fine in the city and at lower speeds, it is when I reach around 50-75 MPH my truck will randomly jerk when I release the gas pedal (it feels as if it would down shift hard). If I keep giving it gas at those speeds it runs and shifts fine. At lower speeds it runs fine.
-No engine lights.
-Transmission fluid is good.
-All the gasoline is new (drained fuel tank because someone told me it might be bad gas (still jerks).
-Last major job was a month ago I had to remove a header because an exhaust manifold bolt broke into the head, and I had to drill/tap out.

I drove it for a long time since and this problem didn't present itself until today (Replaced both head gaskets), it had an engine light on before the head gasket job for an evap leak and a cylinder knock (bad sparkplug). The codes cleared themselves out after I drove it over 30 miles. I have driven it for over 200 miles since, I rechecked the wire harness and everything is connected properly.