1985 having partial acceleration problems please help

I need help, I have a 1985 cougar with a v8 in it. When we got it, it ran good, but now you can be driving it and when you push the gas to go up a hill it doesnt go it kind of pops and then it wont go so you have to pull over put it in park and then go again and it does fine, until another hill. We changed the fuel filter, and it was full of rust. The car has been sitting up for a while and we put a gas treatment, and fuel injection treatment in the gas. Afterwards we were told that was a big mistake since the car had been sitting up for so long, the treatments just broke loose the rust in the gas tank. We were told by friends, and family to clean out the tank, or that it might be the fuel pump, or transmission filter. When the car is running you can hear the fuel pump kick in so im figuring its not the fuel pump, but could use some input from someone who knows more about this. Please help, I love my car and I want it to run good.

if it is an automatic tranny try replacing the fluid and filter.

if it is an automatic tranny try replacing the fluid and filter.

We have replaced the fluid and filter we are going to clean out the tank this weekend to see if thats the problem. As long as youve got a full tank it wont do it but as soon as it hits a quarter of a tank its gonna do it

maybe it has some kind of fuel pickup problem or something. not sure

"Pop"? Intake back fire? Check the timing and set it to what Ford says it should be at for that car.