Pinto Car Club of America

 It's a 72 with the stock 2 litre. It runs well when it's cold and for about 30 minutes. After that amount of time it begins to run rough and buck like the fuel filter is clogged. I have replaced the filter and it is getting fuel and spark. Could the coil be breaking down after it runs for that amount of time?

Very possible, since it runs good for 30 mins that really doesn't sound like a fuel problem.
Does it run rough at idle? If you put it in neutral and rev it is it smooth? Or is it just doing the huc-a-buck under a load?

Runs good at idle and while revving from idle until warm. Once it warms up it starts doing it.

Take the air cleaner lid off and when it's running rough spray a little mist of carb cleaner into the carb. If it's a fuel problem it will smooth up, if it's an ignition problem it will most likely stall.

It runs fine at idle and under load until I drive it at a constant highway speed for 20 minutes or so. Then it starts the herky jerky like it's starving for fuel. If I stop and let it sit a few minutes it will run okay for a few more minutes until it starts up again. Once I am off the highway and at surface street speeds it also becomes okay. This morning on the way to work, I stayed in the slow lane so I could get more stop and go driving and it behaved fine all the way.

It still has the points/condenser combo on it and I have installed a mustang sender unit in the tank.

It's more like something in the tank is wrapping around the fuel strainer and blocking it. But there is nothing but some rust flakes in the tank. I guess the tank needs to come out again and be cleaned at a radiator shop.

I had a simular issue with my car. It ended up being the distribuitor and or the points/condenser ( I replaced the whole distributer. If your points are not adjusted to the correct " dwell " it will cause the same conditions as you mentioned.