Bow Just Got Slower?

[YosemiteSam]

My Samick Sage just got slower for some reason.  Same limbs, same arrows, same everything, including a clicker to the same draw.  But the arrows are landing point-on at 20 yards instead of 6-8" high, which is where it's been for the last couple of years.  The change happened in the last 2 weeks as I didn't shoot it for a little while (kept unstrung during that time).  I'm trying to figure this one out.

Heat?  We're at 35+ days of triple-digit heat.  I keep the bows in my office where the temps fluctuate between 77 during the work day at 85 or so after I leave for the day.  I never leave them outside.

Age?  Could the limbs just be getting old from use?  I shoot this bow almost daily.  Do these bows wear out after a couple years of heavy use?

Set?  I'll unstring it if I'm not going to shoot it for a while but often leave it strung for a week or more as it is a regular shooter.  I thought these kind of bows could take being strung for long periods, though.

I know it isn't humidity.  We max out at around 25% and have been running the a/c daily for the last month.

Anything else it could be?  Should I be looking to replace the limbs?

[TomMcDonald]

Is brace height the same?
Could the nock point have been moved inadvertently?

[YosemiteSam]

Is brace height the same?
Could the nock point have been moved inadvertently?

Good ideas -- checked & all is well on those issues.  But as I was checking, it reminded me that I had just replaced a few nocks in the last 2 weeks & they hold pretty tight to the string.  I'll see if I can loosen them up with some hot water & see if that takes the speed back up a notch or two.

[YosemiteSam]

Loosening the nock fit seems to have done the trick.  Thanks for jogging the brain a little.

[Cyclic-Rivers]

It could be a form issue  If everything else with the equipment checks out.  Only way to really know would be to hook hot up to a machine. 
As far as form, it's best to shoot with someone who can watch, you'd be amazed how often people can keep the same anchor point but lose an inch in draw length.  I hope you figure out what is going on..