Remove the bolt and look at the locking lugs where they contact the reciever, are they both making contact? Most factory rifles dont. Just seen one the other day. That will cause stringing!

Jon2- You've brought up an interesting point. The "I want to believe" factor...(We're going to HAVE to come up with a name for it!) I've been combating it for a lot of years. My solution has been to "code" the load, so I don't KNOW the load until I go back to my records. Many of the guys at the range think I'm 3/4 nuts because I can't tell them the load, but I'm not loading for THEM...I'm loading for the rifle.
I can still tell the difference between the bullets, but not every plan is perfect.
Almost(over 95%) of my ammo is fired over a chronograph, so I keep track of that variable,too.
Have fun,
Gene.

My .25-06 will stay under 3/8" 100 yds if she stays cool but as soon as she starts to warm up she walks all over the paper.

Not sure what the twist rate is in your barrel but you may try a heavier bullet. My dad's savage will shoot just about any 115gr bullet under an inch. His is a heavy barrel so it doesnt heat up very quickly.