Engine bogging

In 3rd gear only. When I step on it, it seems to beg for something. 1, 2, 4 & 5 seem okay. Happened on the interstate coming home tonight?
Any ideas? Okay second day. I think it's a vacuum issue, based on advice from smarter people than me.

What kind of MR2 are you driving?

If it is turbo, I would suspect either ignition or detonation.

V6 5vz.