[old man jimmy]

When you say "It doesn't want to tach up through the gears" Does it fall on it's face like it's running out of gas? If so the floats in carb. could be set too low. Or could be a fuel pump or filter problem. When your foot is in it, and all four barrels are open, it's going to take fuel to keep it going. Need more info. on what it is doing. Or if it's back firing when it falls down. Or if it kinda sounds like a jake brake. Could be many things.