So i picked up a 1976 dodge power wagon for a work truck. I put alot of time and monye into her but i still have a lack of power thing going on. It realy has me stumped. Its has a 225 L6 w/2 bbl and I'v replaced the distributor, dis. cap and rotor, wires, plugs, carb and all ignition boxes.The air gap and timing are set to specs. My idle is sweet and 1st and 2nd gear are strong. My problem is 3rd and 4th gear. I get a flat spot when i shift in to the higher gears and try to acclerate. It's real bad when im on a hill. She just hesitates like crazy. I have to down shift and slowly give her gas till my rmps are up, then the hesitation goes away. I'v tryed addvancing the time and adjusting the air/fuel mix but just can't get it right. Any help would be appreciate.

Check the fuel system. Sounds like a fuel supply problem. Might be a clogged sock filter on the pickup in the tank.

could be fuel, try setting the base timing to 12-14 degrees, it is a 225 l6 so its still gonna be weak

Your stating that the flat spot happens under acceleration, or when going up a hill. One thing you might check on is the float level. If it is too low, that could be your problem. Hope you figure it out.