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2008 F650 6.7 Cummins

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I bought a used F650 a few years ago. 2008, Cummins 6.7/Allison auto, pre DEF. This was a real upgrade from my 06 F650 with a 5.9 Cummins. The 6.7 was stellar! More power, the throttle peddle was actually more than an on/off switch, could actually merge with traffic onto the highway, I was happy ... then I had what appeared to be issues with the turbo variable vane system sticking. Common issue, I know. Poor performance, always seemed to be "out of breath", no power going uphill, poor throttle response, back to the 5.9 feel. Replaced the turbo system, could hear the turbo running correctly again, but ever since this happened, nothing has brought back the original performance. So the turbo was replaced, the EGR has been replaced, new injectors, the manifold pressure sensor for the turbo replaced twice, some other stuff, can't remember it all. Nothing has really changed, still poor throttle response, no power going up hills loaded or unloaded. Seems ok in town though not like when I purchased the truck, but getting on the highway, or going up a hill is still a lesson in patience and humility. I do not dare to make a pass at highways speeds unless I can see for at least a mile, even then I usually do not even try. One shop asked if it has ever done a "regen" cycle, and I have never had it do that (I am the only operator), but after asking, he seemed unconcerned. Two different shops have looked at this truck several times and tell me that there are no codes now, and that everything is "within specs". But still the truck does not perform like when I purchased it (at 125K). Now has 170K. There have been slight improvements when things have been fixed, but I am a long way from the performance it used to have. It functions still as it is, but man I wish it would run like when I bought it ...  Any suggestions?

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