Few beginner questions
 

Well I recently picked up a 2003 gmc Sierra 2500 crew cab for a toy/camper hauler and come to the conclusion that I need a better system in it. Im getting 2 JL 13tw5 or 2 alpine type r thin subs, which would you say is better and I what's a good amp to power them. For speakers I have yet to take doors off to make sure but I think they are 6.5 speakers in front and 4x6 in rear (correct me if I'm wrong), what are some good replacements for them as well as a good amp to power all 4. Last question is do I need to do the big 3 with this set up or run a cap? Thanks in advance for any help or suggestions :)

Before you get a bunch of other people's opinions on a) what would sound good to you and b) how to spend YOUR money, go have a listen to the subs you mentioned, if you can. If not, try finding some reviews or reading around on forums such as this, to see what poeple who are using them think.
Sound is SO sujective, what any of us tell you to buy could sound like crap to you, wasting your time, money and effort.
Any 4-channel amp whose 4ohm RMS power output matches the midrange speaker's RMS power ratings should work; you have to spend quite a bit of money on an amp, and have all the peripherals of equal quality, to really tell the difference between any 2 decent amps.
Caps are a waste of money.
If you're drawing sufficient current (mostly the sub amp) upgrading the big 3 is cheap and easy; highly reccomended.

I know I didn't reccomend specific gear but you asked for opinions, and this is mine.:)

Here is a good way to start; determine the maximum space you have for the sub stage, then choose sub/subs that will perform best in that space with your desired goal, budget and how it would compliment your front stage (which is also dependent on your overall goal of the system you want to set up).

Listening experience and research is vital !

Well I did what you said and went to listen to the subs in person, had to travel few hours cause my town sucks haha. I decided to go with a alpine system, 2 type r 12" shallow mount subs. This brings me to my next question, there will be 3 amps for this system, 1 per sub and 1 for the speakers, I know I need a distribution block for the power, do I run the 0 gauge wire from the block to the amps as well? Or should I use something else there and just 0 gauge to the block?
http://www.onlinecarstereo.com/CarAudio/p_28404_StreetWires_DBX30.aspx
Or
http://www.onlinecarstereo.com/CarAudio/p_29764_Tsunami_TSDB-8014.aspx

Which would be better for my needs here?

Forgot to say what amps I'm using, using 2 alpine Pdx 1.600 one for each sub and 1 Pdx 4.100 for the speakers.

Got help locally thanks for the replies

Sorry no one was able to get to you sooner.

As you likely found out, yes you should use a fused distribution block and likely smaller wire to the amps. I believe the PDX take 4ga wire.

Alright, rather then make a new post I figured I would use my existing one. I bought everything have it mostly mounted and speaker wire ran, im working on the big 3 now and need some help, simple questions but I cant find an answer anywhere and want to make sure I do it right. Do I leave the existing positive wires connected and just add the 0 gauge from the positive on battery to alt? The negative from battery to frame I know I pull stock out and replace with 0 gauge but do I leave the other stock negative on and just add the new one from engine block to negative on battery? Sorry for the noob questions, I tried searching and couldnt find. I did find a video that it looks like the guy leaves the stock ones and just adds the 0 gauge in but I cant be sure. Please help as I am stuck here and do not want to move on until im 100% sure im doing it right, thanks!

........

Welcome to the internet. You want immediate answers, go talk to a pro and pay for their time answering you. There are several threads on here alone about this topic.

In short, it depends. Usually you can leave all the factory wiring in place and add the three new cables.