Early jets did suffer from Mack tuck. Later jets do seem to have the problem designed out. I was always suprised the 707 didn't have a Mach Trimmer considering it's susceptability to the problem. The Handley Page Victor had a Mach trimmer and it predated the 707 by about four years. The early 737s and (IIRC) the 727s had them so a retrofit shouldn't have been too difficult.