Another Power Loss Question

[TClanton]

Ok guys. I was hoping that I had found my answer with the AC/power loss discussion earlier this week, but the AC doesn't seem to by my problem. I am having major power loss on steep, long grades that I wasn't having before. I've only had this SD for a little over a month, but didn't experience this until a few days ago. Both the fuel filter and the prefilter have been recently replaced. The only thing that has changed is that I finally got down to the point of putting in new fuel and refilled at a station near the interstate, hoping that that would mean fresh diesel. I put in fuel system cleaner and fuel enhancer (provided by my mechanic) when I filled up. Could the cleaner have loosened some gunk that is clogging something? Once I am on flatter ground or crest the grade, the speed comes right back and no problem. I couldn't make it up a hill today and had to back down and find a less hilly route back to the office...no small feat in Bham.... ....

Even then, I had to catch on on-ramp and almost didn't make it up the hill. Took the next exit doing 25MPH. Then it was fine. Turning the AC on or off doesn't really seem to matter. What am I missing here? I did find out that my aux fan isn't coming on in the middle of all this....HELP!