When pushed going up hills, loses power and "bangs" like a backfire. What is causing that?

You got a bad connection to the fuel pump inside the tank.

is it a manual or auto?
if manual it could be the weak clutch. check for the diesel filters.otherwise its diesel pump need to be done.

Yes it would. Take a can of Brakleen and with engine running spray around intake manifold. If it is the source of your leak, the idle will go up.

it sounds like a fuel issue are their any codes in the system how is your fuel economy is their a drag on the system is it only going up a hill

sounds like the catalydic converter is plugged/partial blocked- replace

Either the timing is off of one of the valves is leaking

I would guess transmission or fuel pump. The question is when it loses power does it **** or like has a muffled backfire, if it does I would go with the fuel pump, may even need a tune up. I would tune it up first as that is the least expensive and go from there. Hope this helped tim

Replace fuel filter, spark plugs and definately plug wires. You should also make sure intake filter is clean and clear.

It sounds like the timing is off but moore likely it's caused by the point gap being to close due to wear on the rubbing block.
The gap of the points effects the timing.
You probably need to clean and adjust the points.
If that doesn't work try replacing the points and if the old one are pitted, replace the condenser also.
If that doen't work check the coil.

fuel strauner inside tank