You need to make sure that only one of those statements gets executed at any given frame. Something like this (not tested):
if (time < key(5).time){
linear(time, key(3).time, key(4).time, value, value+comp("OUTRO 3 TEXT HITS").layer("TEXT CENTER CONTROLS").effect("1st TEXT CENTER ADJUSTMENT")("Slider"));
}else if (time < key(7).time){
linear(time, key(5).time, key(6).time, value+comp("OUTRO 3 TEXT HITS").layer("TEXT CENTER CONTROLS").effect("1st TEXT CENTER ADJUSTMENT")("Slider"), value);
}else if (time < key(9).time){
linear(time, key(7).time, key(8).time, value, value+comp("OUTRO 3 TEXT HITS").layer("TEXT CENTER CONTROLS").effect("2nd TEXT CENTER ADJUSTMENT")("Slider"));
}else{
linear(time, key(9).time, key(10).time, value, value+comp("OUTRO 3 TEXT HITS").layer("TEXT CENTER CONTROLS").effect("2nd TEXT CENTER ADJUSTMENT")("Slider"));
}
Dan