Brother Iām surprised no one till now has mentioned here that 2nd gear low pickup is one of the famous problems of Liana since its launch.
Pakwheels is filled with many threads (even from way back i.e. 2007-2008 time period) discussing the same issue.
I too have kept Liana for over 02 years and used to drive it on both CNG & Petrol. The issue was persistent on both fuels and was more noticable while using the A/c.
I generally shift gears at or under 2000 rpm (regardless of any car) and on Liana I used to feel severe sluggishness in 2nd gear. Afterwards I used to shift from 2nd to 3rd at around 3000-3200 rpm (with a heavy foot) and I felt a bit improvement in the pickup.
For reference I currently have a 2007 GLi and I shift from 2nd to 3rd around 1800-2000 rpm and never have felt it underpowered or sluggish.
So to conclude if you usually shift gears at lower (under 2000 rpms) then try shifting at between 2800-3200 with a heavy foot and see if you notice any improvement.
As for compression test, you can still get it done just to be on safer side.