I'm not familiar with cabelas arrows at all but at that length I wouldn't think you'd be underspined at all , maybe a little overspined which is o.k.

Anyway , you should still start from scratch again. Concentrate on perfect form and try keeping your bow arm straight a few seconds after the shot.

Was your tear getting worse or staying pretty consistant as you moved your rest?

You can also try moving the rest the opposite way thats suggested by Eastons tuning guide. I've seen it work on plenty of occasions.

When I refer to form I'm not suggesting that your form is bad , I'm mostly refering to hand torque. I've helped alot of my buddies achieve bullet holes without moving the rest by concentrating on form/follow thru.
A few of them refused to believe that it could be torque by pointing out the relaxed (open hand) grip they used. Then while watching them shoot I noticed that the open hand grip at the start of the shot was replaced by a death grip after the shot. I think they thought their bow slings were for looks. After getting over the scare that their bow was going to fly out of their hands if they kept a relaxed grip all the way thru they started shooting bullet holes.
I'm not sure if this is your problem or not but I thought I'd give you some things to consider.

Also , after you start from scratch again. If your still getting left tears try backing up from the paper. I'd bet your getting bullet holes at 7 - 10 yards.