Diesel Bombers - Sticking throttle, Sluggish response

I have a '96 Ram2500 4x4 with 120,500 miles on it. This truck sits ALOT. I think I put 2000 miles on it in the past 2 years. I just put new brake lines, calipers, wheel cylinders, drums and shoes on it. I did front wheel bearings, rotors and pads last year. It's always started VERY well, -20 degrees and it'll start without having the oil heater plugged in. I started having some starting problems and found rotted out fuel lines, replaced those - problem solved. Recently I've been having trouble with the throttle sticking. I already had the recall done, so that won't help me. The throttle cable is not the problem either. I checked everything I could and found only one thing. I'm new to diesel motors so bear with me...there appears to be a valve at the rear of the injection pump. It's hooked by a metal rod to the lever that the throttle cable goes to. The valve seems to have a sticky spot. If I grab a hold of the rod and move it rearward it moves smoothe for about 1/2" and then it gets gummy, then frees up. When I let go of it it only returns to the sticky spot. Then I have to grab it and pull it forward. Is there anything I can do? Also my brakes don't seem to be as firm as they should be. I bled them as you do any other vehicle but they don't firm up???

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By the way, the sluggishness I forgot to mention, as I start to lay into the throttle, there seems to be a lot of movement in the pedal and no change in rpm.

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I'm not sure what it was, maybe a combination of things, but I put a new ball stud on the lever at the rear and cleaned and lubed all the other joints and a couple of new springs and it seems to be working again. I still need to find the air leak in the fuel line, it's losing prime, and my brakes still suck. But I can drive it down the road with out it running away.