q power steering problem?

[qship96]

for the last few cold mornings,the steering effort has increased,and after making a turn,the wheel is slow to return to center-all this goes away after a few minutes of driving-any ideas on the new problem? fluid is annually flushed with M1 atf,since new,and boots are in good shape.temp has been around 40F in the mornings.149,000 miles on Q.