88 f-150 5spd dual tanks, how do i tell which pump is goin out? when i start it it idols halfway decent, then when i give it gas it kinda dies then when i let off it kicks in. and i also have a backfire in my intake....what causes that? how can i fix it?

First check that fuel filter.
A Fuel pressure gauge will test the pumps.
The intank pumps are low pressure if it has a high pressure pump on the frame.
The low pressure intank pumps will be around 5 lbs of pressure.
Does it read the same pressure on either tank?
Depending on engine you should see 40-60 lbs of fuel pressure at fuel rail.