Well the worst I've done is hit the speed limiter on the LA3 turbocoupe computer, which is set at like 116 mph or something. That was in a 1990 ranger with a 2.3T, M5OD, 3.73's and 215/70R15 tires. The engine was at about 4200 rpms in 5th.
I only did it because I was stuck behind about a dozen cars on a 2-lane highway and nobody would pass and I was late and getting angry. I'll never do that again though. Old trucks were never designed to go that fast from the factory, let alone after they get 20 years and 200000 miles on 'em. Besides, I'm married now and it would not be fair to my wife to take that kind of needless risk.