Engine will not redline

I have a d16a6 1.6L in my 89 civic hatchback, when i try to go above 5,000RPM all it will do is sputter, and it acts like it wont do it!, but when i go downhill it seems to go at a higher RPM like 6,000 or close to it! I have changed the fuel filter, plugs, distributor, and put injector cleaner in it,and it is not a blown head gasket!, and there are no codes on the ECU! what else could be wrong with it?? Someone help me out here!