1989 300TE stumble/hesitating/hiccup

[dka-66]

My 89' 300TE has stumble/hesitation/hiccup (not sure how to actually define it) under hard acceleration, it seems to happen in the 1000 to 2000 RPM range and as far as I can tell it happen happens around 1200 and 1700 RPM........Also, every once in a while under hard acceleration it bogs down but above the 2000 RPM point it will accelerate fine.
It does not seem to make any difference if it is hot or cold, it may be slightly better at the first start of the day.

It has new Beru plugs, Beru wires, distributor cap and had the head off for a head gasket, valve guides, and valve seals.

What would be the best place to start looking? I have found threads for stmbling, hesitation, and hiccups but I cannot find any threads that match what my wagon is doing.