my @number = qw(3.34 3.67 4.75 4.98);

my $maxdiff = 0;
my @index = ();

foreach my $i ( 1 .. @number-1 ){
    my $diff = abs( $number[$i] - $number[$i-1] );
    if( $diff > $maxdiff ){
        $maxdiff = $diff;
        @index = ($i-1,$i);
    }
}

if( @index ){
    printf "%f: %f , %f\n",
        $maxdiff, @number[ @index ]
}