:-)
Yes I have cruise control on my latest car and it is strange to have your suspicions confirmed. Folk really do speed up as you approach them from behind, presumably because they ave to undergo the affront to their dignity of being overtaken; and really do overtake you and then slow down once they have pulled back in ahead.
Yesterday I passed someone on the motorway only to find, as soon as they got into my blind spot, they decided they wanted to speed up and undertake me. Irritating though that is, I was even more perplexed a few miles later when I caught up with them again.