Well, I’m still a bit dubious – how old were the tires?
The only way I can think of to get four tires out of round would be to do a serious, tread laying panic stop (which might have happened after just before said accident). But I think that would show up well before 75 mph.
My theory is that Mechanic 1 did a static balance instead of a dynamic balance on the tires. It’s hard to know if Mechanic 2 took you for a ride or not without actually knowing the condition of the tires that were replaced. But if they were older than 3 or 4 years, it’s just as well that they were replaced.
This thread was started last Thursday. Are you still alive? Nearly every poster has told you to take your rattletrap to a real mechanic. Have you done that? If not, do it!
If you’d rather, however, you may regard your problem as a message from God that your days are numbered. I can only hope that when your cosmic number comes up in the power ball game of life, you quietly hurtle into a bridge embunkment, and that you do not go careening across the median strip and take me out.
My grampy would have been proud that I was able to make a logical guess that your problem was tire related. He worked at GM for longer than I’ve been alive. I hope you got new tires!