  We report kinematic shift and strength variability of C IV broad absorption
line (BAL) trough in two high-ionization X-ray bright QSOs SDSS J085551+375752
(at zem ~ 1.936) and SDSS J091127+055054 (at zem ~ 2.793). Both these QSOs have
shown combination of profile shift, appearance and disappearance of absorption
components belonging to a single BAL trough. The observed average kinematic
shift of whole BAL profile resulted in an average deceleration of ~ -0.7 +-
0.1, -2.0 +- 0.1 cm/s^2 over a rest-frame time-span of 3.11 yr and 2.34 yr for
SDSS J085551+375752 and SDSS J091127+055054, respectively. To our knowledge,
these are the largest kinematic shifts exceeding by factor of about 2.8, 7.8
than the highest deceleration reported in the literature; making both of them
as a potential candidate to investigate outflows using multi-wavelength
monitoring for their line and continuum variability. We explore various
possible mechanisms to understand the observed profile variations. Outflow
models involving many small self-shielded clouds moving probably in a curved
path provides the simplest explanation for the C IV BAL strength and velocity
variations along with the X-ray bright nature of these sources.
