I bought a used 2001 ram 1500 last year. Couple things driving me nuts. First my door sticker says the truck should have 245-75-16 tires. The spare (looks like the original factory Goodyear) is a 265-75-16. The truck now has 285-75-16. I think they are making the truck perform like crap. No power and crappy mileage. I don’t care if the truck looks "cool" I just want it to perform on the road. I pull a bass boat and drive back a forth to work and that’s it. With the 285 tires the speedo is off about 10 miles/hour. It should only be about 5 or 6 according to my calcs. I bought a hypertech III programmer and put in the correct tire. This fixed the odometer but not the speedo. It is still about 5 miles/hour off. Another thing the cruise control acts like it is making the truck down shift. I hope this problem goes away with the proper tires. It is not really down shifting more like slipping but does not do it when I control the throttle. Thanks for the help.

 

The tire sticker must be generic. My truck with the sport package came with 265/75 tires and the door sticker doesn't match. Good chance the spare is correct. Mine came with aluminum wheels and a steel spare, which is still there.
The cruise issue might be from the RPM's being low and instead of steady pressure on the pedal, it waits till the speed starts to drop and then applies throttle to compensate. if the RPM are low it is harder for slight throttle to correct and will downshift to catch up. On mine if there is an approaching hill at low rpm's I just give the trottle some help until the top and let the cruise take it from there. Before the modifications, tires, gears etc. on mine, it would do this running 55-60 MPH with the RPM's under 1800.

 

My truck has 265 Kelly Safari's on it. I think when it comes time to get new ones I'll drop back down to the 245's for a little better performance and mileage. I also want to get rid of the slow speedometer issues.

 

I have the exact same problem. I just bought an 01, 5.2, 4x4, 3.55 gear, with 285-75-16 on it. The tires really do look good, but it saps the truck of all of its pulling power. My door sticker calls for 225-75. Depending on what numbers you use, if you percentage the 3.55 gear up by the % change in the tire, it causes the effective rear end gear to be about 3.20 - 3.30 or so. This would be fine for flat driving on interstates at 70-80 mph, but it really sucks for anything else. My speedo (and odometer) is off by about 10%, 5 mph @55. My cruise control sucks like yours, constantly downshifting on every hill, even on interstate at 70. When the truck approaches a hill, and bogs down a little, it seems like the computer is a little confused, panics, and hits the throttle a little too hard, causing downshift. The downshift is a very busy, irritating process, where it releases the tc lockup, down shifts, then upshifts to OD, then re-locks. (i think).

Here's what I do. When i start the truck, i immediately turn off OD, and drive around town this way. At about 45-50, its turning about 1700, 1800, 1900 rpm and the truck has the power to go up and down hills. Only when I hit a highway or a flat stretch and about 55 do I bother turning OD on.

I was thinking about getting a hypertech or superchips to correct speedo and hope for a little change in tuning/shift points, but you indicate its a waste of time and money (lots of money).

We probably only have 4 options.
1. Change the rear end gear (and front if 4x4) to a lowered gear, say 4.10. Note this should reduce mpg.
2. Change the transmission gearing. I don't know anyone who had done this, but it should be possible.
3. Put smaller tires back on.
4. Learn to live with it

I'm surprised that the hypertech did not correct both your speedo and odometer. I thought they always went together. Anyone ?

If you already are aware of torque converter lock i apologize, but, we have 4 speed auto trans (46re), and if you count the shifts, it will feel like 5 gears. The extra one is tc lockup. Watch you tach at shift. An actual shift will hold rpm constant, and you will hear the momentary slip and feel the engine load change. When the tc locks, you will see about a 300 rpm drop on the tach, but it still pretty much feels like a shift. When I turn OD off, I get tc lockup in 3rd. When I turn OD on, I don't get tc lockup till 4th(OD). I don't know if this is normal or if i just have a screwed up trans.

I have a question though about your crappy mileage. Since your tires are bigger, and each revolution is covering more ground than stock, then your speedo and odo are registering lower than actual. So checking gas mileage against under-registering odo will understate actual mpg. if you factor up your odometer mileage by the 5-10% and then calc, you will get true mpg. Do you think your crappy mileage is based on understatement of odometer, or caused by engine constantly up/down shifting. I would expect your mpg to be the best its ever going to be with the bigger tires, covering more ground, and the higher effective rear end gear (3.20-3.30). You know, these trucks are not known for getting the best mileage, especially the 5.9.

anyone else ?

 

I was planning on putting the 265 tires on next time and getting rid of the hypertech. But I think the speedo will still be off by about 5 mph. Using my gps the hypertech put the odometer right on. Does the same sensor control the speedo, tach, and odometer? From what I found out there is a sensor at the rear wheel. My calcs show about 13.5mpg driving back and forth to work. 21 miles averaging 50 mph. Not much city driving at all. This is probably not to bad for the truck. I didn't buy it for the gas mileage I guess. This is my first dodge and so far I love it. I did have to put a new fuel pump on. Thanks for the help so far. I really enjoy reading all the other threads.

 

w/odometer mileage corrected for 10% error - driving around town 40-50 w/OD off I get about 14. Hwy @55-60 w/OD on i get about 16-17.