Ford/ Mazda 4x4 Auto has developed a skip/ buck at low RPMs while in high gear. on 1999 Ford Ranger

Have replace plugs wire twice, EGR Valve, intake gasget twice, and fuel sensor.

Asked by for the 1999 Ford Ranger
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is the check engine light on?
No not at this time... Just had a vacume leak test with smoke and checked plugs, wires again still skips when warmed up but not when cold. It is like a miss or buck in high gear 1500-2000 RPM.