Randomize darfst du nur einmal auf rufen und schon gar nicht innerhalb einer Schleife kurz vor Random.
Zitat von
Delphi Hilfe:
Randomize initializes the built-in random number generator with a random value (obtained from the system clock). The random number generator should be initialized by making a call to Randomize, or by assigning a value to RandSeed.
Do not combine the call to Randomize in a loop with calls to the Random function. Typically, Randomize is called only once, before all calls to Random.