Vail Pass

Vail is high country. Your turbo won't even kick in until 1500. Not enough available air. Turbo then can't help you engine braking going down. Can't help you going up. Need to run much higher RPM's than down below (sea level). You should have (and probably did) notice it was pretty doggy through Denver if going west. Eisenhower Tunnel, Vail, Glenwood Canyon--run your RPM's up for all of them. You can actually 'shift' going down by changing your engine brake setting, 1, 2, 3, depending on what you've got. At 1800 I'd increase to 3, at 15 I'd decrease to 1. Very cool.

 

I'll take a wild guess and assume you are a company driver in a governed truck. Most major companies will dial in the governor for maximum speed, like 62 mph. What a lot of new drivers don't know is that they will also set the governor on maximum rpm for various gears under top gear.

For example, in my brand new '15 KW T680 with 8 speed (+ granny low) 7th is governed at 1500 rpm. I CAN push it to about 1800-1900 rpm for a while (about 15-20 seconds) and then it will fall back to 1500 rpm. It feels like a loss of power when climbing a hill, but it is simply the governor kicking in for maximum sustained rpm in that gear.

Last winter I picked up an O/O's old truck and drove it for the company. It was governed well above the limit for a company driver, a 13 speed. I could climb hills nicely at 1700-1800 rpm. When I took it into a company shop they got on the computer and I watched as they reset the parameters. Top speed was dialed down to 62 mph and they also set 1500 rpm as maximum after 20 seconds in every other gear.

So it may be that your "power loss" is simply the computer program kicking in to keep maximum sustained rpm's at 1500.