I have a 2002 7.3 with auto trans that I bought new- I have babied it and taken impeccable care of it- it only has 112,000 miles- the transmission was replaced by Ford at 93,000 miles- I have used it in the past to tow large trailers nd I know what an impressive work horse it is....I know how it feels when it is running right under a load- last summer when pulling my 5000lb camper to the mountains I noticed a loss of power when going up a hill, didn't want to downshift, no power- took it to my mechanic and he found that there was a split in the hot side intercooler CAC boot- we were sure that was the problem, and it was fixed. They had scanned everything, no codes. It seemed to be running fine and towing well but at the time was only towing on the desert floor- that was the last time I pulled my trailer into the mountains for the season- I stayed on the desert floor during the cooler months and my truck seemed to tow fine, thought the problem was resolved. I pulled my camper into the mountains this past weekend and noticed when going up an incline it would begin to slow down and when I depressed the pedal to get it to drop into a lower gear, there was no further throttle response- I would get to about 55 mph at 22000 RPM"s and my foot was on the floor- no lights lit up on the dash- engine temp and trans temp did not move...this is not right. It seems to be running smooth without a load...idling smooth...no chugging sputtering or stalling- it's just with a load that it is no longer downshifting and pulling with lots of pedal to spare...what happened?? It is all stock except for a Donaldson Blue 6637 air filter- I have never had any problems with it aside from a new transmission from ford at 93,000 miles- the one thing that makes me a bit suspicious is 5000 miles ago I had the fuel filter replaced because I smelled diesel fuel....the filter was pretty dirty and diesel was seeping out from around the gasket even though the lid was secure....the drain valve was completely blocked even though it had been changed 12,000 miles earlier....at the time I couldn't understand how the filter could get so gummed up because I am religious about changing the filter by the manufacturer specs....and why would the drain valve be completely plugged(Nothing came out when opened) when it was leaking and replaced only 12000 miles before?? I stopped by my mechanic and relayed the whole story to him- they had no immediate thoughts, it's just going to be a witch hunt, he's going to scan it but can't get me in until next week....so have to drop the truck off for an indefinite amount of time so they could trouble shoot....he is supposed to be a 7.3 diesel expert and he didn't seem interested in discussing the possibilities....I felt a little brushed off- I am pretty upset over my truck not running right and was hoping to receive a little reassurance that this is a problem that he has seen before. I take impeccable care of my truck and was hoping that maybe people on this forum could give me some suggestions or stories if they have experienced something similar. Would appreciate any input!