A few hours into a 6 hour highway I was making in my 145 I noticed the engine temp dropping to well below normal (this car normally runs warm and can overheat in stop and go traffic so this is abnormal). Soon after, I noticed that the engine had no low end power, but would rev fine once it was above 3000 RPM or so. It would start and idle fine (and had low end torque until about 1250 RPM) but had no midrange. Eventually, I couldn't even get it up to speed without going through the gears up to 3rd or 4th and then dropping it down to 1st or 2nd to get the revs high enough to have power again. I had noticed a slight misfire in the midrange for the previous week but nothing this bad. I was hoping to make it home and diagnose the problem before it got this bad.

Any ideas? I was thinking it could be vacuum leak but it doesn't seem like anything I've heard of before.