I recently picked up 2 spare driveshafts for my Tracker. The slip yokes LOOK exactly the same, everything looks exactly the same.  They have the same number and pitch of teeth ( later model) the two double wide spaces. The original yoke slides in easily and smoothly, while either of the two spares I have will not go in more than an inch before getting stuck. Any ideas? Maybe a wear issue with the outputshaft? Thanks all.   

I've had an issue with my Silverado where I hear a "clunk" when I start off from a dead start. Turns out there is a burr that developes in the slip yolk that catches on the output shaft. The fix is to gently run a file down each spline. Fixed.

I wonder if there is a burr that's hanging things up in your slip yolk. 

Worth a look.

I'll have to get in there with a lamp and magnifying glass. It's strange that both the spares do it ( won't go in smooth) but not the original. Weird. Thanks for the tip.