Ok, this may be a dumb question... But here goes. My glove box says my gears are 3.55, however when i am on the highway I am taching 2k to make 70mph. i have 285/75r16's with the auto trans. I used this website:http://www.f-body.org/gears/ to calculate my gears and it seems to me I have 4.10's. Is this weird?

 

Mine @ 67MPH right on 2000RPM running 305/70/16 and 4.11 gears. the speed i tested with two different GPS.

 

My truck has 3.55s and i'm at 2k right at 70 mph. I have an NV5600

And I have 285/75r16 Goodyear Wrangler silent armors

 

The auto have .69 OD vs .73 6th OD. So auto have slightly lower rpm @ same speed than manual on same gears and tire size.

 

So i guess my glove box tag could be wrong?

 

i run 2300 rpm going 65 mph with 265/75r16s, and i have 4.10s. I have the nv4500 5 spd

 

Is that in fifth gear? according to the chart you should be running 71 at that rpm

 

check your speed with a GPS. Since you have bigger tires you need to calibrate for the difference in tire size, 31" stock tires vs 33" tires.

 

yes that is in 5th gear, and i should put my gps in there just too see where my spedometer is reading

 

the chart shows 71mph running 3.54 gear, with 4.11 should be 62mph +- at 2K.