Strange Question
 

When you put your truck into 4 low, does the speedometer still read correctly? Or does it think you're going faster than you are.

I thought about this the other day. I don't think i've ever really looked at my speedo while in 4 low.

Does any one have any idea, or is it something i'm gonna have to try.

ejr

Your speedo will still read correctly.

It will read correctly because the speed is taken at the tail end of the transmission/transfer case unit right before the driveshaft.