espa.s13

so i just got this s14 around 3 weeks ago. stock KA. the car seems to be original stick not converted from auto to manual. so i drove it like 15 miles to get home and i noticed on the freeway the rpm is really high im going 65mph the rpm sounds like its on 4500 the tach is broken when it reach 3000 rpm it wont go up anymore it just goes up and down. so when i go faster around 70-80mph its feels and sounds the rpm is at 5500 its really weird. i dont know what the previous owner did. now the question is what could cause this problem? is it the differential? tranny maybe?

now on the tranny noise. really high rpm like down shifting. the sound comes from the shifter. my friend in his s14 has similar problem. sounds like grinding rattle noise. could it be just low on oil? or old oil. planning to change tranny fluid might help with the problem.

oh one more thing i noticed when i down shifted and the rpm was really high. i looked at my gauge cluster the temp gauge and the fuel gauge went down. the temp went on C and the fuel went down to E and went back up to normal level when i eased up on the throttle.

any suggestions on whats going on?? thanks.