I am trying to find the cause to a problem. When I first got my car, (06, tc, auto) it use to cruise under 3000 rpm @ 77 mph. Now it cruises at 3000 rpm @ 74 mph.

Can anyone help me why my car does that or is that part of normal wear and tear?

Unless your transmission has changed, I don't think that's possible.

The only difference may be if you're on different size wheels and/or tires.

not to threadjack but where are you located in ohio. im from akron area

it isn't possible unless you've changed transmission ratios, which you haven't.

in top gear, the difference between 74 mph and 77 mph is 3 mph. when in overdrive, the difference between 3 mph is just a couple of rpms.

think about it, the higher the gear the car is in, the more higher the ratio of mph is relative to rpms. so the difference in RPMs between 74 and 77 mph is probably completely unnoticeable on the tachometer.

if the car is cold (not full operating temps for engine, trans, fluids) it will keep the trans from going into overdrive. this will make the RPM higher.

check this again in the spring (or next warm day)