I used to have a 2005 with a 5-speed with the same issue. When cruising at 80mph with the rest of traffic the thing would rev it's ass off (4000rpm). Who ever came up with the gear ratios in the 5-spd trans should be tarred and feathered. I was in the same boat, there was nothing I could do I got sick of it so I traded it in for a car with an automatic, (now does about 3,000rpm @ 80mph).
same problem here with my 2000 gxe. i'm familiar with chevys and fords. with my blazer, i've got a few transmission options i can change to. Can these sentras do the same? does anyone know if the 6-spd trans from the specV 2.5 bolt to the qg18? sounds like a good fix if it does.