I have a 4l60e, 70 mph is at 2600 rpms with 245/5016's. The axle code is GU5.

 

At 62 mph your tach should be just under 2,000rpm if it has the o.e 3.23 gear.Let me know your rpm @ 62 mph.

 

62 mph is at 2100 rpm.

 

Dude, you might have to crawl under the car, spin the driveshaft and count how many turns!

I verified the #'s against www.f-body.org/gears --- 70 mph @ 2600 RPM corresponds to 4.10's, but 62 mph @ 2100 RPM works out to 3.73's?!

What may be throwing the #'s off a bit is whether or not your converter was in lock-up when you checked the RPM's.

Here's something to try. Run to 75 mph in 3rd gear, and see what RPM you're at . Divide by 1000, and you'll have your gear ratio .

 

70 mph in 3rd gear is 3300, I couldn't get it up to 75 because of traffic. I must have the new VTECH rearend-variable ratio and all that- only $4.99 on ebay!

 

Does it come with a sticker.......

 

VTECH diff ... I love it!

Also, just thought I should acknowledge, you said in your first post that the axle code is "GU5". Well, that is the code for 3.23's. I think we can say with a degree of certainty that your car does NOT have 3.23's in it .

That looks more like it would be 3.73's . With 4.10's, it would be around ~3750 to do 70 mph in 3rd.