decided to take it to the body shop so the shop supervisor could give it a class A inspection before taking it in. When I got it started it idled fine. When I started to drive it, it started sputtering like crazy and with the gas pedal to the floor it's top speed was no more than about 15 mph. Gradually it would start picking up speed and only after a few city blocks would it kick in and start running normal . I called my mechanic that built this new engine for me and told him about it, and he's supposed to be coming over to take a look at it tomorrow. From the symptoms I described, what do you think the trouble could be.