Early season velo is often a tick low - temps, still building up arm strength, etc all play a factor. It's barely April, I'm not concerned with 1-2% velo dips to start a year out.
I think one issue Megill is going to run into is the ABS impact on his curveball - As a pitcher, he's at his best when he's at the top of the zone with his heater, and at the bottom of the zone with his curve. Multiple times in save/late game situations he's already had called strikes on curveballs wind up being overturned because they were fractions of inches below the zone. His pitch mix lies on the upper and lower extremities of the zone, and hitters can adjust their game plans to just not be aggressive early in counts in hopes he's not able to find the zone enough to put them in a hole.