Cummins ISL 9 with Alison 4000 6 speed.

I'm a little surprised you have a 4000 tranny as most ISL's came with the 3000. Not downshifting between 65 and 40 is a programming problem... probably because it's programmed for 500 HP.
My combined weight is over 42K and I can climb most mountain passes at 40 in 4th without manually downshifting. On a long climb I will manually shift so if I have to let up on the throttle for traffic it does not upshift. I use the Eco Mode for rolling hills but not for mountains.

"pointrow"......In my previous coach, an 05 Diplomat running 37000 pounds when towing, my 400 ISL, chipped to 450 HP would pull the I-5 grades in California and Oregon in 5th gear at 55 mph plus. I once topped the Baker grade going to Las Vegas (coach was 36000 pounds at the time) at 70 mph.

Fast forward to my new coach, 2014 ISL 450 that weighs the same as you when towing and it's no where near the hill climber my Diplomat was. On my Diplomat, I would just drop into 5th, with the cruise control on and climb. I do the same with my new coach, but it will start to lose steam about half way up. I find I have to get more of a running start and keep working the throttle to try and maintain a reasonable speed. Most of the grades I was climbing before at over 55 mph, I'm now doing between 45 and 53. I try to stay around 1800 -1900 rpms for power. I never had to drop the Diplomat into 4th, but I do with the 2014 at about 40 mph.

Now here is some good news. Mine was really doggie until it hit about 10000 miles and the power started to improve. I'm now at 12K and found on my last trip it had even more power. I don't think it will ever compete with my Diplomat, but it's getting better. I figure it will keep improving until it reaches about 15K.

There is an engine chip (DigiCR) that I added to my Diplomat that can be added to the new DEF engines. It changes the fuel timing, but doesn't leave an imprint on the ECM and reverts back to stock settings at wide open throttle. It worked well on my last coach. I will probably wait until I have 20K on this coach before adding it on.

Sooooo.....with all that said, you're coach is doing what it should. You may want to manually drop to 5th and turn off "Economy Mode" at the base of the grades for better performance.

what elevation, and what size engine and torque ratings? Clogged fuel or air filter?? turbo not working properly?? if you are at 42,000 then this may be all you get.

The ISL9 features common technology with the Heavy-Duty ISX15 and ISX12 for exceptional performance. Common components include the XPI fuel system, a high-capacity Electronic Control Module (ECM) and the patented Cummins VGT™ Turbocharger from Cummins Turbo Technologies. Ratings range from 260-380 hp (194-283 kW)

In the (ECONOMY MODE)it can turn into a dog on some grades.It can make a BIG difference in rolling hills. If you are in rolling hills and regular mode (particularly with the cruise control on), it is common for the transmission to shift down to 5th on the uphill and back to 6th on the downhill. Repeat this process hundreds of times. In economy mode, you will stay in 6th gear unless the hill is so steep or so long that the engine can not pull it without dropping below peak torque RPM.
Every time you start the coach, the transmission is in regular mode. This is the default setting. IF you push the mode button, it goes to "economy mode" AND the light illuminates, your coach may of had the default settings changed.
JR

I-70 has some pretty steep grades east of Richfield, Utah, and 42K lbs for a coach is a lot of weight for an ISL Cummins. So you can expect it to slow down going up those grades.

Now the down shifting is of concern because Allison transmissions will down shift accordingly.

It sounds like you may have the "mode" function enabled. This would impede downshifts.