We just got in a 01 7.3 2wd auto truck with stock 3:73 limited rear. Took it down the highway and it shows 2200ish at 70mph. I always heard and my 03 7.3 2wd X with 3:73's all do 2K @ 70. Why is this truck so much higher?

 

Did you verify the gears? Same tire size?

 

My first thought is the speedo's aren't calibrated on both trucks, so one or both of them could very well be off.

 

Ditto- especially on the tire size if you've already confirmed the same gear ratio.

 

The tires really could be the size of go cart tires or the size of tractor tires and no matter what speed you are actually going the speedo will still read 2200+ and 70mph.

Slowpoke: I am going to take the garmin along today and check the new truck. In my X the garmin show the speedo to be right on, maybe a 1/2 mile an hour off if that. Same in my 6.0 truck and the mini van. But this as well, even if the garmin says the speedo is fast by a little still only tells that the tires may be a bit under size (they are new).

I have confirmed the gear ration according to the tag on the diff and vin. Now while I can't say for sure the PO didn''t change the gearing I see no sign of anyone ever being in the rear diff. In fact it look as though not a single thing was ever done to this truck beside the batteries being changed. The truck just turned 100K miles and a 75 year old man owned it all its life.

Once I get the truck up on the lift I will mark the shaft and turn the tires and count to get an estimate to see if they are 3:73s yet or a 4:10.

I need to run it on AE and do some logs and checks with the truck. Then I need to pull it in the shop and tear it down to the chassis for its "treatment".