Tips on playing fast

I’m learning Whiskey Before Breakfast to play with my family. My dad expects to play in “fiddle speed” which seems to be around 150 bpm. Being that I’m relatively new to playing the dulcimer, I started learning after the age of 60 and I’m not highly talented, it’s a struggle to play the 1/8 notes cleanly at that speed. Rather than fretting each note, it’s more like sliding the noter up the fretboard as I strum. If I do it right the strum comes when the noter is in the right spot. Otherwise the noter might be late and I get two notes as I slide over the fret or even worse a buzz or dud depending on where the noter is when I strum the strings. It’s a bit of a challenge to start strumming that fast and hit all those 1/8 notes by sliding the noter and getting it to just the right spot at just the right moment. 

So far I’ve figured out that I need to be in good position just behind the fret at the beginning of a group of 1/8 notes. If I’m off at the start, it goes downhill from there. Moving the noter that fast often causes me to overshoot the fret. Does anyone have any tips or suggestions to help playing fast and clean? Also I am playing with a flat pick strumming in and out. Thanks Ken