Erratic exhaust temps along with mpg?

Det 14l egr removed ddecv. No reason at all exhaust temps will be okay then go high like 950 plus even bobtailing. Truck will seem to run okay then get lazy lower power. At same time. Cant find any exhUst leaks. Checked cac 3 times its good!!! Pressure tested with caps and gauges so its not that new air filters new fuel filters new injector harness checked ECM wiring for corrosion no signs went over all the ground wires I could find. no injctor missing that I can tell of and uses no oil in 15000mi no smoke out of stacks. Mpg also swings high of 6 to 4.4 spends most of its time in fours i fill to same spot in tank hardley no idleing cant afford to when in fours. dont drive over 65 spend most time slower when exhaust climbs usally drop gear wind up to 1550 rpms to try pull them down a little mind u that this even happens on flat ground. Bobtailing also. What am I missing here. Besides its a detroit.

 

No codes. Might just start replacing the sensors or ecm harness heck thrown bunch money on pile already had it up to 5.3 mpg steady then put new air and fuel filters in and mpg went down to 4.3 detroit fuel filters Donaldson air filters. Has no mufflers. And 3/4 of that mpg was empty. Beginning to hate this thing with a passion! First detroit ever owed and will be last one. My 6nz when lost injector still got better mpg then this anchor.

 

No waste gate on turbo bad part is if it sits a little bit like sitting at a long stop light then will run normal exhaust temps for short while then go high don't matter if running high or low Boost. Makes it hard to put on dyno got to get it while running messed up. I did put in New injector harness Because found it was oil soaked in wires also cleaned connector real good with starting fluid bunch of times ECM side wasn't too badly soaked. What's also got me puzzled is losing darn near 1 mpg. Could this thing be running lean or rich? That's y the high ex temps?

 

New cac and holds pressure even took spray bottle with soapy water to it while under pressure made my own test kit with PVC caps a pressure gauge and regulator carry it in truck. Only think didnt check was intake manifold but I don't see any tell tale signs of leaking by any dirt streaks coming off of gasket haven't figured way of putting smoke to it yet.

 

Hits it fast and just hang don't matter if 10lbs or 20lbs boost I don't know if sensor or something in wiring because don't do it all the time normally running down road it's right around 700deg then for no reason jump to 900deg and stay there and when it does that I notice that motor don't pull so well at bottom end then real sluggish and builds up slow whereas when normal exh temps will build fast even down low at 1100 rpm and pull steady. Gone over harness can't c anything bad short of pulling it apart completely. Which if it would stop snowing I will be doing.when I was bobtailing and hit 900 was flat ground doing 58mph not accelerating just trying to maintain speed no wind.