power void at full throttle

[blk924s]

My friend has a modified 1988 toyota celica gt, and acceleration up until full throttle is quite powerful, but once the pedal is fully depressed there is a feeling of a power void!
The modifications include a cold air intake, headders/full exhaust lightweight flywheel/ crank pulley,, all sensors are stock, also has a brand new cap/rotor/ wires/ iridium plugs/ injectors (rebuilt)/ fuel filter, and all of this on a rebuilt engine.
We don't think any of these things have created this power void though, because the feeling has been present ever since the car was stock. All I can think of is the computer is doing something funky once it gets the full throttle signal. Any ideas? Thanks for your help!