My Jato is slipping really bad, replaced clutch, still slipping, turned slipper clutch adjustment all the way and and still car barely moves and free revs, this is strange, kinda new at this so I need some help please!

Try spinning the spur gear, does it push the truck forward?
If not, then check you drive shafts and weel hubs. If those seem fine, than the problem might be in your tranny.

Is the spur gear turning when you rev the engine?

If it is, look at the drive shafts going to each rear wheel. Are both of them turning?
-If one shaft is turning but the other one isn't then you probably have a broken roll pin in that axle (the diff is diverting all the power to that wheel since it's the path of least resistance).
-If neither shaft is turning then the problem has to be inside the transmission, most likely a stripped gear.

I can spin the spur gear by hand and feel a little friction, but the truck doasnt move forward much, the drive shafts dont spin and the hubs and pins are good

Ok... Time to open up the tranny...

Damn, thanks for info guys

upon further inspection and removing the rear bulkhead for no reason, the problems is the driveshafts, where it connects to the trans the u-joints have like a oval shape that fits over the metal shafts on the tranny and both were rounded out, a very weak point on jato drivetrain, Jato owners beware! Its time to upgrade to the Low Mass Metal Constant Velocity Driveshafts

Aren't the stock shafts plastic? That just looked to me like a problem waiting to happen. 'Course I guess it really isn't all that much worse than dogbones.

Called Traxxas and cussed about it, turns out there supposed to be pins with setscrews through the yolks that connect to the tranny, mine were never installed, so they are sending me brand new ones. I thought something didnt seem right there.

The set screws probably just came loose and fell out. If they were never installed in the first place then the car would never have moved. Although Traxxas should learn to use thread lock...

Manufacturing defects... what to expect after receiving the first batch.

Not true because the housing of the drive shaft is shaped the same as the part it attaches to. Like a half circle. So it would of went for a while until the plastic gave. Also the system on the JATO is a bit better than the stardard Ive dealt with. The screws are long and have the pin connected to them. So it threads in one side goes all the way thru and the pin comes out the other side. There alot harder to fall out than the old style with the little screw that goes to the flat spot on the little arm and stops. Hard to explain if I knew the names of the parts it wouldnt be so hard.

You could be right, I am probably thinking of my steel output yokes where the yoke are round, not shaped like the stock ones are.