At about 3.5-4k in 5th gear my car appears to eith stall or hit some fuel cut. The engine just revs as though it is in neutral. I have to downshift to forth in order to get thinkgs back to normal. My speedo/odo don't work all the time, so I'm sure how fast I'm going, but I know it can't be the speed governor. Anyone know the problem? Could it be something stupid like a clogged fuel filter or is my ecu messed up?

Also noticed that the revs fluctuate between 500-and 1500 rpms when stopped in 1st sometimes. An ideas?

Thanks
Josh