What do you guys think. I have a 3.73 axle ratio and in 5th gear my speedo shows 100 kilometers an hour or about 62.5 miles an hour. I know my speedo is correct as I have a GPS. I want to know if you guys think I have the right pulley on alternator. I changed pulleys because I didn't think my truck was reving at 2500 rpm as old pulley showed at same speed. My truck is K2500 - NV4500. Thanks in advance of any info you guys might have.

Seems a little high rpm. I have those gears as well and mine revs at 2100 rpm at 100 kph with lock-up engaged. Guess it depends on your tire size.

I have 4.10's and at 65 MPH I am at 2500 RPM's almost exactly, so I would say you are not running that many RPM's.

I think you must have the wrong alt pulley. Get someone with a scanner to see what rpm the ECM is showing.

You should be turning around 1950 RPM's @ 100 KM/H. I know my factory tach is high by 10% all the way across it's travel.

Are you sure it has 3.73 gears?

K2500 may be if-fy about 3.73. Need to check RPO codes to see what it has. I think GT3 or GT4 is the code you need to find on the sticker, check FAQ's for more RPO info, and which one is which.

I run about 2200 rpm with a 4.10 and 265 rear tires

GT4 is 3.73
GT5 is 4.10

My 6.5 with the factory tires and 5 spd tranny was a hair under 2000 rpm at 100kph