Thanks everyone for your suggestions. Jiffer, I'm all over the interval gig. I need to find a route with a few longer stretches.

I've been riding alone lately which I actually enjoy because I can focus on my ride instead of on someone else's speed. Nonetheless, I am sort of disappointed in myself. I think I'm in great cardio shape. Not sure why it is such an effort to go balls out for longer periods. Wish I could blame the bike. Ha!