Darrin,
As a twinky owner, with many twinky friends, we all talk about our speeds. I find it's hard to compare because when i say i set her up at 23/2400 75 ROP and get X speed, then my friends does similar, he's always running 5 kts faster, the only way to take away the little difference in settings was to run side by side, everything full forward, cowl flaps open and guess what, we were dead even!
If i or my gauge is off 1" or 50 RPM, or mixture etc, my airspeed can decay quickly.
To check your guage or serious riggin problem, maybe go out and run balls to the floor.
I do this for a very short period, 15 seconds or so....that should be enough to get to speed.
Warm up, climb 2000', slowly get up to speed, then climb 50' higher so you can pitch down to get on step quickly, full forward, level off, hold till airspeed tops out, should be 15 secs....
ON very warm days at 3000 DA, i get 167 kts, on very cold days i can get 177 kts!
Just another thought.....
steve