silverado power stering

Hi all. I'm new to this forum but I sure am glad I ran across it while surfing.
I own a 1998 chevrolet 1500 EXtened Cab.4x4 I love this truck. She is my pride and joy and has take care of me and my family well for the past 11 years.
Recently after returning from a long road trip I was making a left hand turn onto my street and noticed the steering loosen up as if air in the power steering line. It was brief and ended 1/8 of the way thru the steering to make the turn.
The problem has since continued and has increased. It happens now after truck has set for a while and if i turn the wheel in both directions at idle . also feels a lot tighter when driving and the wheel dosn't spin back to center as easily after a turn. i recently replaced front bushings break pads master break cylinder fluid flush and a front end alignment. Power steering fluid ck. ok but a little dirty. I fear it is increasing.
I don't know what the problem is. and thought I would ask for some advice here prior to bringing her into the local GM dealer. :0( I always get the feeling the dealers are "replacement" focused anymore vs "repair" oriented.
thanks in advance for any help or advice.
best regards,Car Repair Talk's forum.