What went wrong?!? kinda long

It has been a while since i have been to this forum, but you have always come through in the past.
My truck just past 68,500 (not a typo) this past weekend and I wasn't sure for a while if it would make it to 69K or not. The rear tank had #1 left over from the winter, the front had #2. I have used Power Service fuel additive from Car Quest for more than two years. Mods are listed in my sig line. Superchip is 50HP.
I took a trip hauling the 10,000# 5er over the holiday. Just over 300 miles one way to Fairbanks on the Parks Highway. Lots of hills. Twice, within a few miles from home, the truck just *died* when I was slowing down for red lights. While on the front tank I found that going up some of the steeper hills I would get hesitations, bucking/vibrating, and could not get it to run over 30 MPH, and it really hated down shifting into 2nd gear. No real smoke either...just really rough. Once, I downshifted out of overdrive to pass another rig @ a top speed of about 65 MPH. Just as I pull back in, it starts to hesitate and vibrate...it would only go about 50 MPH (flat road) for about 3-4 miles, then it was fine. I noticed all gauges fine, but my pyro dropped down to 350-400 during this time...that has never happened before. Switched tanks somewhere at this time. Further down the road, while cruising at about 63-64 MPH the truck just died. All gauges shut down...nothing. Shifted into neutral and coasted to a safe stop. Would not fire while coasting. Once completely stopped, it fired right up. Made it the rest of the way to Fairbanks without any more problems (about 50 miles).
I spent the weekend in Fairbanks and did a little tinkering. I have a CPS in the glove box, but this really seemed fuel related so I did not replace it yet. I drained the fuel bowl half way then pulled the filter...it had 5,000 miles on it. Looked like some fine black particles in the bottom of the bowl and the filter was somewhat black. Went to NAPA and got the *special Price* WIX filter for $38. Filled up with #2 in my two empty tanks.
The truck ran flawless the rest of the time. I did NOT use the Power Service additive in either tank. Power uphill, in 2nd gear on downshift, stayed at a steady 40 MPH up the steepest hill (it use to do 45MPH on the same hills with the same 10K# 5er, but heat made me back out of it...still had power though.
I normally get about 13 MPG when not hauling, and 10 MPG when hauling. It has been this way since I have done all my mods. This time (without the additive) I got 8.3MPG on the way home. Otherwise, it ran smooth as a top, quiet as a Powerstroke can be, and no bucking.
I figured it was a fuel problem from the get go. Probably some of the crap they call diesel at one of the stops I made was part of the problem. The other is the #1 left over from the winter. I think the filter change was what helped...but since I didn't use the additive, I can't rule that out 100% either. If it was the CPS, I would think it would have just died and never started again.
Any suggestions, questions, or ideas out there? Thanks for any comments.