Hi and Thanks in advance for all help/advice.

I replaced a rear shock on my bike. When first installed it was eye to eye 6.5" (165mm) after a 1 hour ride, I noticed the shock was a good bit shorter and I had to physically pull it back out by holding the rear tire down with my knee and pulling on the seat. I checked sag before riding and it seemed ok. I assumed it was under pressurized because I hadn't pumped it up for some time (had been working on it a while) I added air when I returned home and now the shock is only eye to eye 160mm.

Shock is cheap, but hey, I got 3 daughters!
2010 RST Element LO ( I know, RST...)