When you say PT6A-42, speed problems, you're talking Ng, gas generator speed. When you talk propeller RPM problems, you're talking Hartzel.
Presumably this is on a King Air B200?
While the two are linked mechanically, the propeller is largely independent. Not enough information is provided. From your description, you just have a propeller that's slow to move, and that could be several things from an internal mechanical wear issue to the wrong grease, to just a rigging question.
What is your gas generator doing? Does it hesitate, surge, or otherwise do anything abnormal? How does it move in relation to the other engine...temps coming up the same, fuel flow looks the same, just a propeller hesitation?
Are your condition levers in high or low? (Bear with me on that one...I'm answering off the top of my head at the moment, and I've been in a number of PT6 powered airplanes recently...each configured differently...My last King Air 200 flight was a few years ago now). Is this occuring on the first flght of the day or subsequent power applications? Have you been cycling the propeller and exercising it before doing this? Does your airplane have a chip detector, and are you doing oil analysis...and has anybody changed oil brands lately? Notice any grease or oil around the propeller, or along the propeller shanks? Have you noticed any propeller hesitation in reverse, or transitioning across the gate?
If you're getting engine hestiations, not just propeller hesitations, a number of problems could also be present, from a P3 air leak to fuel control bellows to filter or pump issues. Temps normal? Ng normal? Are you running a trend monitoring program, and if so, are the trends changing at all?
