Never ending problems

It started with the check engine light coming on. Ran the codes,came up 172 O2 sensor lean. Replaced it. Truck has 248,000 miles on it. So it couldn't hurt. The check engine light would not reset.Driving down the highway 65mph. Check engine light went off. Truck started losing power.Heard a popping noise when stepping on gas. Once the CEL came back on, the truck had power again.I'm thinking it might be a fuel problem. So I tested the pressure.First time both tanks well within range.Second time, the front tank pressure was low. She starts fine.Idles fine. When I step on the gas peddle it revs good, when I release the peddle it feels like it wants to stall. Both tanks.I changed the fuel filter Yesterday. Still doing same thing. Could it be the throttle position sensor? Any ideas.:banghead: