The problem is that you are getting the same value everytime you do an assignment for each run of the loop. For example:

Sample data:
 foo
 bar
 baz

First time through loop
    $TRACK = foo
    $pager = foo
    $service = foo

Second time (etc)
    $TRACK now equals bar
    $pager now equals bar
    $service now equals bar

etc..
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TIMTOWTDI but this would work..

$datafile = "CheckUPS.in";
open (DATAFILE, $datafile) or die "Input data not found.\n";
@text = <DATAFILE>;
close (DATAFILE);
$TRACK   = chomp($text[0]);
$pager   = chomp($text[1]);
$service = chomp($text[2]);

print "$TRACK $pager $service\n";
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