2000 Ford Ranger Fuel system

Engine Performance problem
2000 Ford Ranger 6 cyl Four Wheel Drive Automatic 163K miles

While making a long 4.5 hour trip with a trailer in tow I filled up with regular gas at my starting point. An hour or 60-70 miles down the road I pulled into a small town when the rpm's got below 2500 the truck began to buck and bog down. So I replaced the Fuel Filter which was filthy. It worked ok, still hesitating, but once on the highway and RPM's were high there were no problems 50-60 miles later as I pulled into another town and RPM's went down the same thing happened. So barely pulled into autoparts store and they gave me the diagnostics which stated the fuel mix was too lean (sorry forgot specific code). So banged on fuel tank relieved pressure, unhooked battery to let reset then tried to get on the hwy again. Barely got on but once on it was ok. Next town same thing the truck actually just died this time though. Once at a gas station I put about 3 gallons of regular gas, a fuel treatment bottle, unhooked the batt. For reset, and then another 4 gallons of high octane. Got back on the road for the last leg of the trip. After 60 miles got to my hometown and expected the truck to die again, however it didn't. It wasn't running great but it was running. So the next day I rented a fuel system pressure gauge to check fuel system psi. With the ignition on I could hear the fuel pumping whirring for about 2 seconds but the gauge read zero. Then I turned the engine on and let idle. Slowly the psi reached 53 psi and didn't get any higher. It took at least 3 - 5 minutes of idling to get that high. To make sure I repeated the procedure and got the same reading. So I went for a good drive driving speeds ranging from 20 to 80 mph with no problems what so ever. The only thing I noticed was the sound of a lifter or a tapping of one of the valves that is very distinct and was not as loud before. So what do you think should I replace the fuel filter again or should I replace the fuel pump? There is a big difference in prices as you probably know. Thanks