Truck has a good running 360 and the backfiring is the only problem. The only time it will do it is going down a hill trying to hold a constant speed. If I let off the throttle it won't do it, if I accelerate going down a hill it won't do it but if I keep the throttle at one position it will start backfiring like crazy. It just turned 200,000 but other than this it runs great and doesn't burn a drop of oil. Just changed plugs, wires, coil, cap and rotor about 5000 miles ago and it was doing it before everything was changed. Had it hooked to a scanner and no codes came up.

Backfiring is a sign of a lean condition, probably from a lack of fuel. Fuel filter is probably clogged. You can get fuel to pressurize the fuel rail but when in constant demand the volume drops and causes a lean condition.

I am not sure about a 2002 but my 94 Ram has an in-tank pump/ filter combo. I replaced both at the same time when the time came. I had been having backfiring issues, and the final straw came when I was trying to run 70 on the interstate, it wouldn't do it.

Edit- Rockauto shows an inline filter for your 02 rather than the combo unit- if you do have to replace the pump stay away from the spectra, I put one in a Cirrus that lasted 9 months.

Obviously check fuel pressure/flow like stated BUT also be sure about:

1. the condition of the plenum gasket. If its original/high miles, plan on a Hughes plate

2. Scan it for codes. Had a magnum 5.2 that backfired and it was a mix of problems: crud in the injector filters, corrosion on the feed for the oxygen sensors and a bad plug conenction.

Just seems a little odd that it ONLY does it going down hill holding the throttle in one position. 85 on the freeway it's fine, 25 around town it's fine but if you start going down a hill it's either speed up or completely get off the throttle or it's going to start back firing.