First thing you need to do is get the ICP sensor back in operation. You can argue tht it runs fine without it, but you are likely overworking the IPR to the point that it could be the problem. If you're tired of replacing it, relocate it to a better location on a hard line, or convert to the later passenger side valve cover location.
So the next thing is, the tuning of the engine is highly dependent on the feedback from the ICP. As a tuner, if you asked me to write a tune for your truck and told me you had the ICP disconnected I would not tune it until you fixed it. Most tuners will take the same stance, and if you get a tuner that tells you they will write a tune that "tunes around" the ICP, you're not dealing with a very knowledgable tuner, and you should realize that if they are willing to cut corners to get your money, then te rest of their tuning is not likely the most developed or refined and they would be someone to avoid.
Towing at 75mph, you're asking the engine to work at a moderately difficult load. In order for the engine to operate at that demand, you really need all systems functional. You need a functional ICP to know if your HPO system is operating at the correct pressures. Fix your truck. There are solutions that can prevent repeat future replacements.
The Current Truck (Oct-2013 to Present):
1999 (Early) F-350 Lariat, CCLB, SRW, Black/Tan
7.3L Powerstroke, 4R100, 4x4, 3.73, 37x13.50-18s, '05 Axle Swap, 6" Fabtech lift, GTP38 "D66" turbo upgrade, SCT 4-position chip with custom tuning by me, Straight Piped 4" down pipe through 5" dual stacks, N-Fab full length triple steps, Pro-Tech cab guard and tool box, louvered 5th wheel gate, Hella 500 Fog and Driving lamps, much more to come...
The one I'll miss, (Mar-2009 to Jan-2014):
2000 Excursion XLT 4x4
6.8L V-10, 4R100, 4.30, 285/75-18, 271whp / 388wtq
The one I won't, (Jul-2005 to Sep-2012):
2005 F-350 XLT, CCLB, SRW, 4x4 FX4
6.0L PSD, ZF-6S650, 3.73, 35x12.5-18, 4.5" Lift