Dodge dakota when i start off and floor it, it does not go past 1500 rpms?

[Joe]

Truck runs great once you get going and at regular speeds but it is slow at accelerating, Since its a automatic the truck feels like it runs on third gear then shifts to the overdrive, I'm not to sure how explain it, but when I start driving I floor it and it does not go past around 1500 rpms, after catching speed then the next gear kicks in, and the rpms start going higher, the reverse works fine and the 1 and 2 gears work fine, so I'm not sure if somthing is wrong or its governed