The feed pump and lift pump are one and the same. It's built into the injection pump... If the lift pump is failing, then the injection pressure will be consistent or adequate. When the lift pumps goes on a non-electronically controlled rotary pump, the symptoms are lack of power at moderate and higher RPMs even though things are generally pretty good at lower RPMs.
Make sure there are no air leaks in your fuel system! Put clear hoses to and from the injection pump and the spill tube to the return line and look for anything more significant than the odd air bubble.
The timer control valve is an electromagnetic valve that is part of the injection pump. The spill control valve (it's round and black and sits are the rear of the injection pump) spills fuel to alter injection volume.
The only other thing to try is the Throttle Position Sensor (TPS) as it feeds info to the injection pump via the computer. It does have some effect on tranny shift points, but that is otherwise controlled by the TV cable (kickdown cable).
In reality, the injection pump gets all the throttle position information (from the sensor) by way of the computer. It's really a drive by wire system, but somewhat archaic when compared to more modern designs. The throttle plate is there for EGR purposes primarily... there is another small butterfly valve that opens and closes immediately upon sensing throttle position changes from the base (closed throttle or idle) positions - also EGR related.
I hope I'm not creating more confusion here... really, when these things go wrong, do the basics first (air and fuel filters, check the TPS for a smooth waveform on a lab scope) and then install a new injection pump when all the more basic diagnostic stuff fails to make any improvement.
You can also check the injection timing with a diesel pulse tester and a timing light, but without known good base values it will only tell you if you're close or not. The timing is set by the computer from input values that come from the crank angle sensor and the injection pump - the only things that can go wrong with the timing are being out on the timing belt or the pump being installed with the marks not lined up (between the block and the pump body - which are not likely to go out). The computer is the only other factor in the equation...
In reality, all these tests take time (and cost money). For the cost of the parts, and the amount of labour involved, replacing the pump is something that should be considered fairly early on. These pumps are considered to be a throw-away item, though there are a few (rare) shops with the ability to service them. However, the cost of repair would run more than the cost of replacement with a new unit.
~John
