Evil bike..?

[Popoki_Nui]

I swear this bike is evil, or hates me, or something. I just don't get it: it's the lightest bike in my fleet, and should be the fastest. It has nice 700c x 23 road tires, decent enough running gear (Shimano 600), and weighs a whopping 19 pounds. Nice wide range freewheel.
Yet the longer I ride it, the heavier and slower it gets. Honestly....I can't figure this out. By the time I've spent an hour or two on it, it feels like forty pounds of lead pipe on concrete wheels. I bought it as an unrideable wreck, and spent ages rebuilding everything. All the bearings and new, well lubed and adjusted, and run smooth and free. No brake drag. Frame is straight and true. (Had some fender rub today, but it behaves the same with or without fenders) Everything's just fine mechanically, but at the end of almost every ride I swear I'm towing a hundred pound sled behind me. Today I was tempted to hurl it into the sea and walk home.
Anyone ever experience anything like this?? I am SO frustrated.....

~Sherry.