http://204.186.93.64/Pinions-48P.htm

If those don't work out, I've got a 5mm bore 48p brass pinion on my 1506 I'll sell you. It's either 21T or 22T.

LOL Thanks. I just found the same site right before you sent it to me... Here's another site that sells them just incase you ever need it...
http://www.rcpcrawlers.com

Hi now I am runing my 1515 2.5d on 5s and it run very well, I have 2 packs of lipos 5000mha 5s (2s+3s), And now I want to buy anothers lipos, but i don't know what buy...... I can buy 2s+3s in series or 5s + 5s in parallel. What is best option?

Hmmm I don't know if it's safe to connect 2 lipo packs of different cell counts. I always make sure both my packs are identical if I'm running them in series.
It all depends on what you need. Runtime vs saving money. 2 packs ran in series might be cheaper but they will not run as long as 2 that are run Parallel. So I feel it's all up to your wallet.
One last pointer... running series is always better when you are racing someone or trying to reach top speed... 2 3s to make a 6s will be lighter than 2 6s packs....
Hope this helps!

Nothing wrong with running a 3s in series with 2s, if the cells are the same type and usage. That was my main setup (also using the 1515 2.5d) for about a year, good setup.
I'd say 2 packs in series is usually better than 2 packs in parallel.
Unless you want parallel packs for huge runtime the there won't necessarily be much difference in weight and performance. A 3s + 2s 5000mah and 2 x 5s 2500 mah of the same C rating and quality should be similar.
The main reasons I think the series setup is better is because it's easier to charge and balance the 2s and 3s as one pack. To balance and charge the parallel packs as 1 you would need a 10s charging setup, or make a harness to link the balance taps together in parallel, and I would avoid doing that.
If 1 packs comes unplugged for what ever reason in the series setup the car will just stop. Annoying, but at least everything will be ok once you plug it back in. If one pack comes unplugged in the parallel setup, the car will run of the pack still plugged in. Since you will probably choose lower capacity (and therefore lower amp output), 1 pack will not be able to handle all the load by itself and could be damaged if you kept driving (might not notice drop in performance in low traction areas).
Only reasons I would choose 2 5s packs in parallel would be if they had a good special on them, or you needed a certain size pack to fit in your car (most 2500mah packs will be shorter than 5000mah packs), or if you had something else that you used the packs in.

Ok I never would have mismatched my cells but I guess it is ok.
Well when charging 2 3s packs as one what do you need? 2 balancers I would guess to monitor each pack. Then do you use a parallel adaptor or a series adaptor to charge the 2 packs? I would think a parallel but I'm just asking to make sure...

Connected is series with 1 balancer. You just need a balance harness that will let you do that (easy to make). See the lipo wiring page in BrianG's calculator http://www.scriptasylum.com/rc_speed/_lipo.html

Connecting a 2s pack in series with a 3s pack of the same type is electrically no different to a single 5s pack, except instead of the tabs being soldered to one another you have an extra piece of wire to join the middle cells together. Same goes for balancing

See this is why I get so confused with this. The link you gave me sais charge in series, here's a video of a guy saying charge parallel... WHich one is it?? lol.

http://www.youtube.com/watch?v=Iv6dD67SUew

For packs of different cell counts (2s + 3s) you have to charge in series, you can't connect packs of different voltage together in parallel. The guys says that about 15 seconds into the video as well.

I don't think the average charger and balancer setup can do everything that the Xtrema setup in the video will do, so it's easier to charge in series usually. You could charge the packs in parallel, but as far as I know you wouldn't be able to balance every pack at the same time like they did.

Ok I see. I have a blinky balancer and 2 3s 4200 Neu lipo packs on the way... I'm going to get on the search for the parts to make a y harness for the balancer now.
Thanks.

I hope by Y harness you mean turning it into a 6s lipo as far as the balancer is concerned...

I mean balancer Y adaptors to balance and/or charge two batteries at the same time using one balancer... Patrick led me to the diagram, now I have to find the parts to put it together.

A series Y harness to connect the packs in series to the charger, and some male/female balance plugs to make the harness for connecting the balance taps to the charger is what you require- just follow the diagram and you wont go wrong, which is more that can be said for some traxxas forum numpties who did it wrong and ended up shorting out their packs...