I strongly suspect that the uninit'd var perl is complaining about is $_->{TEST34}. I suggest checking your vars to be sure.

use Data::Dumper;

my @list = ();
my $lastc_33 = '';
my $lastd_34='';
my $last_33='';

......
print Dumper $_->{TEST33};
print Dumper $lastc_33;
print Dumper $lastd_34;
print Dumper $last_33;
print Dumper $_->{TEST34};


if( $_->{ TEST33 } eq $lastc_33 && $lastd_34 =~/8/ && $last_33 =~/00/ 
+&& $_->{ TEST34 } =~/7/ && $_->{ TEST33 } =~/00/ )  {

}
else  {
          $lastd_34 = $_->{ TEST34 };
          $last_33 = $_->{ TEST33 };
          push (@list, $_);
       }
[download]

If that still doesn't show you where the warning is being generated, break up your if statement so that you can see which piece of it is generating the error.