[suicideneil]

Okay then, lets take a look at this.

Provided you get good Nimhs, there shouldnt be any issue running them with the Neu- that said, good nimhs can cost almost as much as some lipos. If you take a look at the swang, zippy, and True RC lipos, you will see that a 2s pack can cost as little as around $60, so using two of them in series will be as good, if not better than Nimhs.

Anyway, gearing.
I know Mark uses the 1515 1y, so hopefully he can give some practical advice, as well as using the calculator. Based on the info you supplied (truck, voltage and motor), then 62/20 will get you about 40mph, which is great really. If you only buy one pinion, then make it a 32pitch 5mm bore item with 20teeth. I would strongly recommend getting the 62 and 65 tooth optional spurs for the emaxx 3905- $3 each or so, and it will give you more gearing options to tweak things. The MMM esc should run cool regardless, as will the motor probably, but its the batts that will tend to run hot if overgearing occurs.

As for general upgrades for BL power, the 3905 is pretty solid. The diffs will be first to give probably, and there are various cheap, and not so cheap options; cross that bridge if/when its required.

Buy a smooth can Neu if at all possible, as that will make life easier when it comes to gearing.

The Hvmaxx was good in its day, but it just cant cut it terribly well anymore, not compared to some of the newer motors and escs. Novak are working on new stuff however, but it wont be out for quite a while, same with tekin.