More power means tighten the slipper clutch
 

So, I went out today and bought a Chameleon 2 19T motor for my Losi XXX-T. Now, whenever I try to accelerate, the spur gear slips. I assume this is because the Chameleon 2 motor has a lot more torque than the old 19T motor that came with my RTR truck. This is normal, right? All I should need to do is tighten the slipper a bit and I'm good to go.

Right?

Any tips on how to properly tighten the slipper?

Are you sure it's the slipper and not the diff?

Take the gear cover off, and hold the right rear tire and the spur gear with your right hand. Now try to turn the left tire. If the slipper spring and nut is turning, then it is the slipper. If they are not, it's the diff.

Tighten the slipper nut until the left tire is considerably difficult to turn using the same test. If it is the diff that is slipping, place an allen wrench through the slots in the outdrive when lined up with the slot in the diff screw, and turn the opposite tire clockwise (in very small increments). The slipper spring and nut should always turn when using the above-mentioned test.

Aaron's right.

Also, did you hear a cherping sound ? if you did thats the diff slipping.