I have been driving a couple of other vehicles lately, so I might be off...but today I got in my truck and took it about an hour away to a kids B-day party, I think the RPM's seemed higher than they used to be on the interstate in the top gear ??

I might be crazy but would any of you other guys with similar trucks check and see what your reads

05 Ram 1500 SLT...N in the VIN
stock everything
265/70/17
3.55 axle ratio if that matters


at 70 mph with cruise, I was right about 1800-1850 RPM's and that seemed high to me

 

Have you replace the ring and pinion in the differential? Or it stock.

 

stock

just changed the oil if that matters ...lol

 

Don't know if this helps but
03 Hemi SLT 1500 QC 4x4
275x60x20 3:55 at 70mph just a touch under 1800rpm.
I'd say 1775rpm exactly.
Al.

 

Based on tire spec for 265/70r17 tires. The rotation is 657/miles. So if your PCM is calibrated for that tire size your RPM at 70MPH should be 1823. If you just calculate based on tire diameter it would be lower but I the spec is taking into account load being on the tire.

 

Looks fine to me. That's where my truck would have been stock if adjusted for your slightly larger tires than mine.

 

RPM is RPM. You can't change it via the PCM. The only thing you can do is adjust the speedometer.

FWIW, mine turns 1,980 rpm at 80 mph. 285/70x17s, 3:55 rear end.

 

I know it does not calibrate the RPM. If the PCM was calibrated with that size tire then the speedometer will read 70MPH when at 1823RPM based on his 3.55 gear ratio and .67 5th gears ratio. What is interesting is that 31.6" tire would normally have 638 revs/mile but the specs on tirerack says that tire size has 657 revs/mile.