What RPM are you running on the freeway? (and at what speed?)

 

That would tell us exactly whats up.

You said your speedo read 80 when going 65? I have 4.88s which read 82 when going 65. You 32" and I have 35" tires. 3.21s to 3.55s would not make that large of a difference.

 

Well I'm back for some more advice fellas.

He went and found the correct 3.21 and replaced the wrong 3.55, but my speedometer is still showing wrong and the rpm is still too high compared to what it was before he put in either rear ends.

I bought the truck one year old, could the original owner have put in another differential? I have a button on the dash that takes it out of overdrive if that matters?

 

Maybe you don't have it in overdrive, that would make a difference?

 

I have that button on the dash, when I take it out of overdrive a little light lights up so I know when it's out of overdrive. Could he have maybe hooked it up wrong so that overdrive button doesn't work?

 

You should see RPM going up if you press the button and the light comes on, that would tell you if button is working.

 

Yes, the rpm goes up.

could there have been be a higher gear ratio rear end in the truck? Higher then the 3.21?

maybe it's all in my head, Ill have a friend go out and pace me to see if the speedometer is reading correctly.

really appreciate the help with this!

 

That or if you have a GPS, my Garmin does really good at showing speed. I wasn't sure until one day I run upon a radar unit that just shows you how fast you are going, it was accurate. They have one of those radar units they put up around the county to show people their speed.

 

I have an android smart phone with gps. How do I use it to see what my actual speed is??

I bet you mean an actual gps unit?

EDIT- Oh there's an App for that :-) Just downloaded it, off to check my speed!

 

Yes my is an actual Garmin GPS that mounts on dash, doesn't have any other functions and from what others tell me is much more accurate. Be careful, more difficult to hold a phone, enter data app needs and still drive. That would be more than I could handle.