tach question

[dzbowtie]

i checked the ground and it seems good. i checked the power to the tach and with key on, it shows 12v. the power wire to the tach is sharing the same key-on source on the fuse block with another power source going to a water temp gauge. that gauge has always worked properly. also, the other morning i was heading to work and the needle seemed to read correctly as i was pulling a hill (approx 3800 with no trouble). then it just kicked back down to just over 2000 and went back to the same behavior of not wanting to pull much over 3000 when im turning rpms. i checked the power wire to the distributor and its connected properly. i removed the tach wire from the distributor and replaced the female connector with a new one, then reconnected it. hopefully this incorrect reading will go away.