just came back from a quick trip and my rpm at 75mph was about 2200 to about 2250, sounds a little low for 4:10's doesn't it?

 

05...I think

 

Wade that may be right since your is a 1500. I know superddd has a 2500 so his may run a little high rpms with a 4:10.

 

i have the 07 clasic...4.10's and at 75 i am am almost exactly on 2500 RPM.

 

I'll check my 07 classic 373 in the morning

 

is gearing not just gearing regardless of the size of the truck? If a truck is bigger/heavier would it not just require more fuel/air/horsepower to move a certain mass? unless of course the transmissions are different, then that would effect engine rpm.

 

Its just like a bike...on speed 5,its ,more powerful but takes more energy.

The general...and all carmakers...go to EXTREMES to find the right "balance"..believe me,if pouring some snake-oil in the crankcase,or moving the timing a fraction would benefit BOTH performance and economy,it would be done

 

would it be possible that my truck has 3:73's even though it is option coded with 4:10's?(like i said before, guy i bought the truck from swore it was a 3:73 axle)my rpm at 75mph seems to be closer to the 3:73 range than the 4:10 . out of curiosity i jacked up the rear wheels today and did the old driveshaft to tire spin, and it took approx 4.5 turns of the driveshaft to = 1 complete tire rotation. this is more in line with the 4:10's.
I checked my speedometer with my GPS today, and my rpm with my scanner and all are right on the money. My tire size is correct, the reading is same as before: 75MPH=2200 2250 rpm.

 

I double checked mine and I hit right at 2500 going 75. The weight difference may have something to do with it: your's being a half ton and mine being a three quarter. I don't know what size you're motor is, but mine is the 6.0. Other than having a TBS, everything is stock from the rear end to the tires.

 

sorry guy's, i guess i should add that to my signature........my truck is a 2000 Z71 Silverado 1500
engine is the 5.3 Vortec, pretty much stock with the exception of a True Flow drop in air cleaner.