I have a rustler running the sidewinder 5700kv and love it. I'm getting about 60 out of it but my spur gear keeps striping. I've went through 3 in the past 5 days. I know its not the gear mesh because the guy at my LHS did it for me. He told me how to set the slipper clutch. I listened and it striped while i was testing. Is this new system too much power for the gears.

Just because the guy at the LHS did it doesn't mean the mesh is right... how much slop is there before the gear was ruined? There should be a tiny bit of play, but not a lot at all.

What do you mean by slop. There is a tiny bit of give

How much space/play/slop is there. If it's too tight or too loose you can damage the gear. You shouldn't be ruining the gear if the mesh is right with a 5700kv motor.

How are you driving it, are you blasting around at full throttle, then slamming on breaks/reverse, then flooring it again, etc?

There is a tiny gap I use the paper method. Most of the time it's at full speed with little stopping

Are you using a high quality pinion gear? How are the bearings on the main (top) shaft of the gearbox?

There's very little load on the gears at full speed compared to lots of acceleration and stopping, so if anything you're putting less load on the gears than most people do.

The pinion gear is traxxas brand. I'm not sure about the bearings. Are they the ones on the spur gear

They're inside the gearbox, you can check that by seeing if there is an wiggle in any direction with the spur gear. If you can move it in any direction you have your source of the issue right there.

I opened the box and all the bearings look good. What else should I check

Did you try wiggling the gear before tearing the gearbox apart? It doesn't matter what the bearings look like, check for a gear that can move.

Also check to make sure the spur gear is fully centered (check the mesh through a full rotation of the spur gear).

It barely moved and can do a full rotation

Barely moved is possibly too much movement... the spur on my 22T (or older XXT as well) can't budget at all except to rotate.

Are there any points where it can move and tighten up the mesh or make it too loose?

I tightened it and it doesn't move at all now

What did you tighten...?

The slipper clutch nut