Sorry didnt read your signature

Then yes - self regulate your rpms to 3kish in 4th gear...

Most people with gearing problems have automatics that are running too many RPMs in 3rd and not enough to stay in 4th

 

Just out of curiosity, what would you (or anyone else for that matter) consider "too many rpm's"? Peak TQ isn't until 3000 and peak HP is at 4750 (when new at least)...so I would think holding 4k for a 5-10 minute climb a few times a week wouldn't be unreasonable...or am I off base?

 

It depends on what gear you are in - I saying when your truck keeps shifting between 3rd and 4th because the RPM's in 4th gear are too low to maintain acceleration..

I guess your question depends on what speed you're going, what gear you are in and if your transfer case is in lo or hi

 

I have the same problem (also in Colorado). Have to keep it above 3k RPMs in order to get over anything at something close to highway speed. The main concern I have in doing so is the coolant temp; if I'm revving that high for more than a few minutes I feel as though I'm getting close to over heating and new heads (237f or so). The first time I took it out and saw this I was ready to rip out the motor before I even got where we were going.

And to the original poster, I agree it's probably your tires. I'm running 305 70's which comes out to about 33" x 12" and it feels like I have no power. Since you chose the larger tires (I like mine too) I'll be watching to see how you solve the power problem.

 

Highway/Interstate speeds...in high range. Basically, to prevent the shifting problem you described, I tend to leave the transmission in 3rd for hill climbs going up the interstate into the mountains (at least the 1 mountain run I have done so far...but that is the plan for the "future"). That causes me to maintain ~3.5k RPMs (somewhere between 55 and 65 mph) for maybe 5-10 minutes at a time but removes the need to fluctuate throttle pressure and the transmissions need to shift.

Edit:
skorten, I didn't notice any heat issues when I did it (only made 1 mountain run so far...only had the truck 1.5 months)...but I was just relying on the factory gauge. The next time I head into the mountains I will use my OBDII scanner to see the real temps.

 

That is an odd size to run on a Discovery. What rims are they mounted on? If it is the stock rims they are only 7 inches wide you do know don't you? For a 12 inch wide tire, you should have 10 inch or so wide rims.

How do those fit as far as wheel wells and such? Did it come to you like that or did you put them on by choice?

That size tire plays havoc with a lot of things, especially the gearing aspect.

Also, when you atart going up steeper inclines, any issues like a vacumn leak or other issues will be magnified when the engine is under more load.

It takes a pretty steep incline to affect how mine runs but I have the stock size tires. Typically at 70mph in 4th gear (automatic) mine is only doing around 2000 RPM's. If I am approaching a really steep incline I go ahead and build up some speed before I get on the steep part and it goes right on up without much trouble.

I do use 3rd gear a lot to keep from having to ride the brakes too much on the downhill slopes. I have a few that I go ahead and drop into second gear but that is due to the lower speed limits in the local areas.

3000 to 4000 rpms should not be harmful to these rigs unless you have other issues. That is pretty much the "Power Band" on these when they are running correctly.

If you are pulling a heavy load that will have an effect as well. But going too big with the tires will definitely throw off the intended gearing and to truly compensate you are looking at drivetrain changes in some fashion.

 

Going 70 MPH you should be around 2500-2700 in 4th gear.. Obviously the smaller the tire and higher the gears the higher the RPM.. So you guys runnin 32's-33's it may push you to run higher RPMs than what you're used to - isnt a terrible thing.

Stock Discos should run at around 2500 at 70.. If your truck is overheating from normal to hard driving on the highway there is something wrong with your cooling system.. I recommend high pressure flushing cooling system and checking fan clutch to make sure it doesnt free spin.

The flip side of the lower gears is off road performance. In lo range your truck will have quiet a bit more get up and go with a sit of 4:11's than 3:54's.

Read here - Mountain Goat and I had this conversation not too long ago

Ashcroft Transmissions - Ratio Calculator

I am picking up a pair of series 2A axles with 4.7's than I am going to convert to 24 spline and fit in the truggy on 33's.. Imagine how that will crawl


I should add none of this has to do with how your truck will preform on hills and mountains. You Disco will be slow and do tons of work to get up hills but shouldnt overheat. My truck gets up to 195 MAX

 

I have 35x12.50's on 8" rims and it is a perfect fit. You can get away with 12" wide tires on 7" rims but they might get a funky wear pattern. A lot of defender guys run 315x75x16's which is a 35x12.50 on 7" stock alloys and they seem to do fine. My concern would be losing breaking the bead while wheeling however the stock 7" wide rover wheels have some of the largest lips and work to hold the bead REALLY well..

Thats my 2c on tires and rims..

Also Danny your truck should be at 2500 at 70.. you should double check that. If you had 32's you'd be doing 2k at 70mph

 

I rarely get it up to 70 since I do mostly local driving. I was just trying to make a point that if it is struggling or overheating at those speeds or rpm's that would be indicative of some problems.

I still have the 235's on mine.

 

Can't afford the fuel consumption at 70 either....