I just bought a 2006 5AT coupe. It seems to have some issues with the speedometer being off. I used a speedometer app that i have found to be pretty accurate while in other vehicles and it has consistently showed that my speedometer displays around 6-10 mph higher than the vehicle is actually going. There also seem to be some transmission issues if i am cruising on the highway going about 80mph consistently the rpms stay at around 3100-3200? Is this high for staying at a consistent speed of 80. Transmission also wont go into sports/manual mode sometimes. Could it be the transmission speed sensor causing all this or is it even correlated?

Those are the correct RPMs for a 5AT at 80 mph. What size tires are on the car? Tire diameter will affect speedo.

If you have it in sport mode on the gear selector it won't engage 6th gear which causes highway rpm to be higher.

255/40r18

there shouldnt be a 6th gear its a 5 speed

thats the correct rpm in 5th gear? (Not in manual mode)

Yes, thats normal. Going 80 in 5th gear will put your RPMs around 31 to 3200.

Yeah, it's part of the reason gas mileage is what it is. These babies love high reving! When highway cruising, I'm always wishing for just one more gear!

It's not the tire size. That would cause your speedo to read 2 mph LESS than speed at 80 mph on OEM 19s.

https://www.inchcalculator.com/tire-...culator_type=c

I have said my speedometer is off since the day I bought it... it always says 35 regardless if I am doing 80 or 90. lololol. Glad to see people are still enjoying these cars. I have my 04, 110k miles. Sits in the garage most of the time. Coming up to 19 years this summer and for the forseeable future, it will always have a place in the garage or driveway for now. I may go all out on a car in the coming year but for now, its staying. Enjoy your holidays everyone!