intercooler boots the bottom ones like to cut on the fender this could be a power loss for sure

the turbo is fine... if you're not blowing black smoke, it's probably not a boost leak, but always check, and I like to kinda bend the fender sheet metal back a little away from the boots to prevent it from happening

really sounds like a fueling issue. weak lift pump, clogged filter, bad overflow valve, etc.

A leak in the intercooler will produce a ton of smoke a WOT. That is how I found mine.
You may not be getting enough fuel. Check your solenoid switch. It is next to and behind the injection pump, down low. You can see a rubber bellows that is the bottom half of the unit. With the ignition switch on, the switch should go ALL the way up. Check by pushing the rod coming out of the bellows up. If it moves the switch is sticking, preventing full fueling. The bellows may be missing, rotted off over time and heat. This will allow dirt to get into the sleeve, preventing full motion. It is cleanable, do a search on DTR, and a bicycle tube will make new bellows.
Has your truck gone through the throttle cable recall? #970, I think, call your dealer.

good call on the fuel solenoid/lever!

I've checked the soleniod, it seems good.

What I was wanting to do was clean all the filters, and replace the main filter again. However, I cannot seem to figure out how to get to the screen in the heater to flush that out.

I will check the intercooler boots. That might be the problem. I don't see any smoke while under load, It does act like boost blow by, or bad turbo seals (I've had turbo charged cars that have failed, and that is what it feels like). But I don't use oil, or have smoke, which is why the intercooler boots would make sense.

Also how would I test my overflow valve to make sure it is good? Is there a place hear that would be cheaper to replace that other than the dealer? I might just do that for piece of mind.

To get to the screen there is a large nut on the bottom of the fuel heater. Remove it and the cover, screen, and some other stuff, including diesel fuel, will all come out. You can buy a rebuild kit from Cummins, $dealer$, or probably someone else will chime in for another vendor. They are not expensive. You can get new overflow spring kit from the same people, again another will probably chime in. To check it, if I remember correctly, remove it and measure its length, should be 1/2" or so, but do some research on that one. A good thing to install is a fuel pressure gauge. Search DTR, there is lots of information about it and how to install one. They can be very helpful.
Can't hurt to check the intercooler boots, but if you do not have black smoke under load, my guess is the boots are OK.
I don't know if this has been mentioned but you can check the turbocharger wastegate line that goes into the AFC. Where it enters the AFC, the connection can go bad. Look for a small black line that goes over the engine from the turbo, between cylinders 5 and 6. Just for the heck of it, block it off completely, what happens? Do this only if you have a boost gauge.

Intercooler boots are fine, removed heater screen, and cleaned, also dropped tank and cleaned both screens in the sending unit. topped off by replacing fuel filter.

All this did give me a little more power, but nothing like it should be.

Now my question is what is the cheapest way, and were would I tap into to mount a fuel pressure guage. So much info on so many different engines to decipher doing a search (mines a 1997 12 valve). From what I did find most drill and tap the banjo bolt on the injection pump. All I see as for that is the overflow valve.

Also is there any way to check the overflow valve? Cummins wants $80 for one, and I hate to spend that if it is not the problem.

Also any way to check the injectors, perhaps they are clogged?

Thank you ahain for all the responses, and help so far.

to check the overflow, pinch off the return line while the engine is running, if it speeds up it means its bad, does it idle rough at all?

Seems to idle fine, I'll try to pinch return line. Thank you.

Getting narrowed down... I hope. I did pinch the return fuel line at idle, and no change in idle. Also took the overflow valve apart, and all looked good, as far as nothing broke, or dirty.

I put a set of vise grips on the waste gate actuator hose, and she has the power it used to have. However, that is not the cure for the problem, and I don't have a boost gauge, so the vise grips came off.

Also put a bottle of injector cleaned in the tank, and it seemed to help, so maybe I have dirty injectors? Again, where would I tap into the injector pump to mount a fuel pressure gauge?

Thank you guys again for all the suggestions, and help.

Traver