look at getting a tcm from a ram 1500 to tow.

I know your pain. I run the GDE full-torque tune and the GDE TCM. I run 255/70 tyres and 3.73 final gears. The problem is the TCM tune and the massive torque hole when it shifts down to 1400rpm. It might give good fuel economy in the city but towing up hill sucks. I'd say get rid of the TCM tune before you try anything else. I think GDE has options regarding TCM setup, including custom setup. Even the stock TCM would be better, wish I still had mine.

GDE has a tow tune that holds 4th gear up too 75 miles per hour. That must be a big hill your driving. Mine holds 5th up most any thing at 1800 rpms. But when I'm towing my travel trailer I could use some help with 4th gear. Hope some people with the tow tunes will respond. I would have aready bought but if you have to send it back for a change from GDE it 100.00 every time. Wanting to get right the first time.
Thinking 4th to 73 miles per hour then to 5th back to 4th at 63 miles per hour. I don't want to shift to 3rd when I floor it. I want it to drop to 4th only.

I'll certainly admit I'm not an expert but I strongly suspect you need to look at more than just the torque curve when trying for efficiency (presumably mpg). Generally speaking mpg goes down as speed goes up in any gearing and certainly the KJ has all the aerodynamics of a medium large brick. Focusing just on power and speed assuming roughly stock tires I suspect the best mpg is going to be achieved locked up in 5th at ca. 1800rpm or about 62 mph although I suppose in theory you might do better at the lowest speed (if you can stand it) you can hold locked up in 5th. Once you push on up toward 70mph mpg begins to drop fairly rapidly. However, if you are on a long downhill run (say from Flagstaff AZ to Tempe AZ) speed and rpm have less influence on mpg.

All I'm trying to say is what the setup and rpm/speed for efficiency will vary from KJ to KJ in large part depending on terrain, towing/not towing, relative amount of hwy/city, etc. Bottom line is there will not be 1 answer for all KJs or even a single answer for "your" KJ.

GDE has a tow tune that holds 4th gear up too 75 miles per hour. That must be a big hill your driving. Mine holds 5th up most any thing at 1800 rpms. But when I'm towing my travel trailer I could use some help with 4th gear. Hope some people with the tow tunes will respond. I would have aready bought but if you have to send it back for a change from GDE it 100.00 every time. Wanting to get right the first time.
Thinking 4th to 73 miles per hour then to 5th back to 4th at 63 miles per hour. I don't want to shift to 3rd when I floor it. I want it to drop to 4th only.

Mine seems to tow better above 2000 rmps. If I drop below then down shift and start all over again. If I run in 3rd the all the time my miles per gallon drops. My rpms are at 2600 all the time. GDE can set your rpm shift point were ever you would like. Call Keith

The tow tune is 300.00 then any changes are 100.00 and mail back and fourth. I leaning to 2200 rpms in 4th gear for my best towing. I towed to Destin Fl from Tulsa at Christmas time. My tank were all over the place. From 12 to almost 17 with a 3000 pound dry weight travel trailer. The big think was holding the speed so close to hold 4th gear. But then shift to 5th going down hills then back to 3rd on the next hill. Maybe next will be that new turbo from GDE really need more power to hold speed,

I have a stock CRD with the GDE ECO-Tune. I was pulling a trailer last weekend on rolling hills trying to go 70 mph against a 20 mph headwind. I ended up putting it in 3rd and leaving it there. It seemed like 4th gear would have given me sufficient torque to maintain 70 mph, but I couldn't get it to hold in 4th, it would shift to 5th everytime I would be going slightly downhill; then when going on flat or uphill grades, the RPM's would drop way down before even trying to shift. Mileage was pretty bad, 12-13 mpg. I really need to find a way to manually select 4th gear over 5th.

If you're driving at sea-level, then the elevation isn't hurting you. Are you running #2 Diesel Fuel? How much does your rig weigh? My stock rig weighs ~4500 lbs with a full tank of fuel, which is heavy for a little SUV. What kind of ambient temps are you running in? Stock tires on the CRD are ~29", so you're losing about 10% of your torque there. You mentioned not wanting to swap your rear end ratio because of high speed driving, how fast do you drive? With my stock setup, I'm only at 2250 rpm going 75 mph. I would say either get a TCM-Flash that holds 4th gear for a long time (running in 4th gear for you would be the same as a stock setup in 5th) or put the 4:10 gears in.

Here are my 2¢ on diesel theory. Diesel engines are more efficient the slower you run them, partially because of friction and partially because the more time you give the fuel to mix with the air the more complete combustion will be. Peak torque is a little different because the faster you run the engine, the more boost your turbocharger is going to give you. More boost means more air which means more fuel which gives you a bigger "boom". In theory, an ideal engine that has the same air charge every cycle would have a "flat" torque curve across the entire speed range. Its things like the combustion efficiency, turbocharger, and internal friction that give the diesel engine its unique torque curve.