I have Just installed a new 2007 Rock Shox Revelation 426 u-Turn shock on my 2006 Trek Fuel EX7.

Last Sunday I went out thinking that I got the perfect setting. Empty the negative (0psi) and pump the positive until I got the desired sag. Then I inflated the negative until just before the fork starts to drop etc etc and the shock was giving me something like 128 travel. However After a few down hills and some rough terrain the shock dropped down to around 118 travel. When I went home I tried to reset it, so I emptied the negative and tried to pump till I got the right sag. I filled up the shock with only 80 psi and I was getting only 10% sag and the recommended pressure for my weight (76KG) is 120PSI. I got the message that recommended pressure is way too high but Im 40Psi less and Im still far off. The final setting was 80 positive and 70 negative. (To get the sag I had to start pumping the negative otherwise the shock would remain ridged. Now my questions are why did I loose 10psi in the first place????? And is it right to be running 40psi below the recommended pressure?

Thanks in advance