Okay folks, I can't figure this one out.

I was driving along the other day nice and smooth, then got on the highway.  Put the pedal down, went thruogh the gears, and the van stalled out on me at 4th.  I pulled over, started it up, merged back on the highway, and the van had no juice.  It felt like it was only running on three cylinders.

I limped home, and went through everything.  The engine appears to be in tip top shape.  It starts quick and easy, has compression, fuel, spark, etc. and sounds just like it always has.  I don't think it's an engine issue.

I checked all four breaks next, and all the wheels spin smooth.

I considered a fouled exhaust, but my system is a straight heaterbox to header setup with no cat. I can't imagine what could go wrong with it.

Is there some kind of transmission/clutch/CV issue that could be causing this? 

Any suggestions?

Thanks, 
Greg
82 Westy