My first time here. I have a Dodge Dakota 2000 V6 3.9. When it warms up it will start bucking when I give it gas. I noticed it does it at the lower RPMS (under 2000). When I'm 3rd, 4th or 5th gear and go up a slight incline is when I notice it the most. It seems to get worse every day. I have changed spark plug wires, rotor, dist. cap and plugs. Still the bucking continues to get worse. I had them check the computer for codes and it said plug wire 5 was bad, so we replaced all the wires. No codes since we replaced the wires. The odd thing is it runs fine when the engine is still cold.

 

10 to 1 its teh crankshaft position sensor. Mine did exactly what yours is doing and thats what fixed it. It would surge and buck like mad for 5 min then clear out. Then it got worse and worse. Would barely get over 45 when it did that.