Mine cruises at 182mph and climbs at 1800 fpm. Now, nothing wrong with
that performance, but still and all...The airplane is straight and
slick. No unusual drag makers. It would seem that I am missing around
25 or so horsepower

I had a similar situation with my RV-4 when I bought it. Climbed OK but was
substantially slower than other O-360 powered RVs. It had a Sterba fixed pitch
wood prop at the time since metal fixed was not available yet. Tried a Sterba
cruise pitch prop with no difference. Got a Sensenich fixed metal 'cruise' prop
when they became available and it was like magic. 15 more MPH on the same RPM.
Climb RPM was 200 less but the rate of climb was the same. I always thought I
needed more power but now I'm not sure. On slightly cooler than standard days
my indicated speed is right next to Vne (215 if I remember). If your RPM and
manifold vacuum is similar to other make and model RVs with that engine then
the engine should be OK. Like mine, it could be the prop airfoil.

Jim