So like the title says, I can't quite get both cables on. One or the other and I get within a couple mm but its not stretching.

WTF? I want to hit whoever said this was an easy install.

C'mon guys, I know somebody knows what I'm doing wrong.

IDK what to tel,l you, I didnt have any issues getting mine on. Have you given all the slack you can at the adjuster on the end of the cables on the grip?

when I installed mine, I had to let a little slack out down by the carbs. I couldn't get enough adjustment up by the throttle. I took my tank off to do that.

^^
You just need more slack to get it over, probably from the carb side of the cable. You'll want more slack on the throttle anyway if you are having trouble getting the cable over the mount. That mount is a bit further or taller than the stock so if you had a little bit of an issue getting the stock tube off with little slack, then it would be a tough one to get the R6 tube on without adjustment.

- Bboy

Thanks for the replies guys. I got it on and it is so fun!

I figured the only place to get slack was at the carb. I didn't want to do that so I assembled the throttle off of the handlebar.  Then I undid the four bolts holding the handlebar on and slipped the throttle back on from the end.  It was ugly and took some doing but it worked.

And I got it all done just in time for it to snow today and I cant ride.   

How much did the R6 tube change the rotation from idle to WOT?

Stock GS throttle tube is 1/4" turn, while the R6 tube is 1/6" turn.

- Bboy