So I have a 65 Fastback, 289 engine, C4 transmission. The Problem is that it shifts late. It seems like it takes a lot to get it to shift to the next gear. For instance I have to go up to 3,000 rpm's before it will shift into 2nd gear. I checked the vaccum line and there is plently of suction coming from it. I've been told to try adjusting the modulator but is there anything else I can do or check? Also, I have an aftermarket edlebrook intake manifold and 4v 650 carb, roller rockers and crane cam shaft so the engine does have some power, but its not fast at all because it takes so long to shift through all the gears. Any ideas?