Mine done the same thing a week and half ago. Only thing was, I forgot to tighten an injector line at the rail. Thinking that was the cause of it......

 

When my truck did this it was two bad injectors. One dealer had me put on a new lift pump, a fca valve, etc. I ended up pulling the injectors & having them tested. Two were bad. I've been driving about six months & the light is off. If you try everything else pull them, it's not a hard job.

 

I have had this problem for awhile (over 2 years). That being said, I have posted and read numerous posts on the subject but have failed to find a solution. I, like STate live in colorado and experience this issue on eisenhower and decending into denver. I found that it only happens when I let off the accelerator going down those hills, but if I stay on the pedal it dont come on.
This issue did not start happening until after I bought the truck in salt lake and the motor blew a month later. I had the motor rebuilt, and was forced to replace the whole fuel system (bad injectors). I know its not my injectors, and the dealer says I have the most recent software. If anyone solved this problem please let me know.

 

What temp thermostat u using, could be to low allowing engine to rum to cool when letting up on accl. pedal, u should have a 190 degree, it sound like cooling or over cooling unless u are in the pedal.

 

My WTS light was coming on, and I would have a P1223 code show up. I would hear 10 dings. Sometimes I would have a CEL with a fuel rail code (I forget the number)

Anyway, I fixed the problem, it turned out one of my injector tubes (#6) needed to be retorqued. Apparently it had somehow loosened up and was leaking.