My Tach question

What should my rpms be at 75-80 with a 3.1 v-6 and a automatic tranny? mine sit between 3500 and 4000 rpms. My crappy ford t-bird with a v-6 doesnt sit that high at those speed so i was just curious it thats correct or if my tach or even speedo is off. To the best of my knowledge the car is stock(engine, tranny and rear end). Thanks for all the help guys. Jess

Have to know what tranny and gears u have. Is it the stock tranny are they the stock gears?

Yes to the best of my knowledge the engine, transmission and rear end are stock to the bone. I need to know is one or more of my gauges is off or if for some reason the car is running at higher than normal rpms so i can get it fixed.