Post your cruising speed numbers:

[DenaliHD66]

I can't really remember what my RPM's would run at with normal sized tires, but with 265/65/17's and going 70mph (according to GPS, not odometer which isn't calibrated) my RPM's are at 1900... which seems pretty damn good. I have 3.42 gears too. 60-65 yields the best range, but that is way too slow for me, but so far on this tank it seems like it will take me a greater distance.

Also, I have a PCM4LESS tune with 87 octane, but this last tank I filled up with 89. It seems to run a bit smoother, have more pep in low end, and as I said before, I'm at 255 trip miles and about 3/8 tank left. Typically I'd be at 1/4 tank at 255 trip miles. Would the 89 octane really be running that much better in my engine right now? I want to get it tuned for 93 just because I see how much better premium runs and how much cleaner it keeps your internals. Post you guys's cruising numbers here too.

 

[tricguy007]

I run a 255/55/18 , 2000-2150 rpm at around 75mph/Speedo (72mph/GPS)my tires are about 1/2inch shorter than stock , 3.42 gears,pcm tune 87 but run 89 or 91 sometimes been doing a lot of idle time still cold out, just filled up at 15 mpg

 

[C-ya]

72 mph GPS (70 speedo), 2100-2200 rpm, 3.73 rear end, 245/70/17 tires.

I normally go 5-7 over the posted speed limit, but I'm trying to get better mileage, so I'm trying to keep the rpm's down a couple of hundred and see if it's better. Seems like anything under 2K rpm is best, but like you said D, too slow!

 

[Shdwdrgn]

Try this page to see what your RPMs should be.

 

[DenaliHD66]

Now that is pretty sweet^

 

[Denali n DOO]

What I'm getting at 75 mph is 2200-2300 rpm, 3:73's stock tire size. I'm pretty close to what the chart says.

I'll have to compare the difference when I get the summer tires on, they are smaller, 255-55-18's.

 

[Shdwdrgn]

It should be spot-on. I found a formula that calculates rollout distance versus circumference, and I would assume the gearing is the same in all years of the 4L60E. If you hover over the radio buttons, it will pop up the ratio used for each gear.

If there are any other transmissions with different gear ratios that should be considered, let me know. It would be easy enough to add that as another option to the chart.

 

[DenaliHD66]

Only thing is, what's the lowest speed you can put into the calculator for it to be accurate? 10 mph and it yields only a couple hundred rpm's, etc.

 

[Shdwdrgn]

Run a scanner on your PCM and see what the actual RPMs are, rather than what the dash says. Then you can compare at any speed you like.