Specialized Fat Boy slicks, Sized 26 X 1.25 rated to 100psi.
I thought I was topping out (spinning out) too, when I started. Got a computer with cadence and learned to spin.
High 70's in 2/7 = 15 mph. Now I'm working on getting up into the high eighties/ low nineties.
Oddly enough, if I make a conscious effort to lighten my pressure on the pedals and just think about moving my feet faster I'll just zoom along. It feels like it should be just the opposite....but who am I to argue with what obviously works.
* Riding with my wife (doesn't like to go faster than 12 mph) is a great way to practice spinning. I just gear down to where my cadence matches whatever target I've set for her speed.