On the 2000 model, I had to remove the bolts that hold the extend-a-bed cage on. Those are the only bolts that need to come out. After that just pull. You do not need to remove the bolts, holding the cables to keep the tailgate up. I believe the 03 and 04 are removed the same way.
I own a 2003 and it's very easy to remove the tailgate. Just loosen (you don't have to take them all the way off) the bolts that secure the cables. From there, just jiggle them a little and they should come off. Then the RIGHT side of the tailgate should slide out. Then take the left side off and BAM, you got it. Just be careful, it's heavier than it seems.
The 2003 Nissan Frontier has 16 valves.
The 2003 Nissan Frontier has a 5-speed manual.
The 2003 Nissan Frontier has an inline 4 engine.
The 2003 Nissan Frontier is a gas-powered vehicle.
The 2003 Nissan Frontier's turning circle is 38.3 ft..
The maximum payload of the 2003 Nissan Frontier is 1312 lbs..
The 2003 Nissan Frontier has a 27 degrees angle of approach.
The 2003 Nissan Frontier has double overhead cam (DOHC).
The 2003 Nissan Frontier is 16 ft. 10.9 in. (202.9 in.) long.
The 2003 Nissan Frontier has a 14 degrees angle of departure.
The curb weight of the 2003 Nissan Frontier is 3240 lbs..
The 2003 Nissan Frontier runs on regular unleaded.