Poor throttle performance

I have a 2004 F150 5.4L supercab. I have added a hypertech lll, put magnaflow exhaust, . and throttlebody spacer, but when I push on the accelerator, there is no performance. It does good 60 - 70 mph, but does nothing at low speeds. Do you think if I changed out the throttlebody it would help? :grinyes: What brand of throttlebody would you recommend? I sure could use some help. Thanks