Hi, my name is Ed. Welcome to JustAnswer!.
Your symptoms make me wonder if the upstream oxygen sensor
heater has lost capacity. An under-heated 02 sensor in this location will leave oxygen sensor voltages high, possibly tricking the PCM into believing your engine is running rich. The reaction would be to pump down fuel trim, removing up to 70% of originally calculated fuel delivery at the injectors in an attempt to correct the (perceived) condition.
I'd be suspicious of the upstream 02 sensor, which my information shows to be a single unit, located just behind the convergence of the two exhaust streams and before the catalytic converter.
The 02 sensor heater is internal to the sensor and will cause a code to set if the circuit becomes completely open, but instances where the heater is still connected... but reduced in capacity... may not trip the code and the performance-saving default that it would provide. Instead, you've got a fuel system that becomes convinced that it's running rich all the time, driving fuel adaptives heavily toward removing fuel and this is likely the reason why the truck runs OK for a brief time after you've cleared memory, until the adaptives are corrupted again.
One piece of advice in choosing an 02 sensor involves the manufacturer. You need to stick with either an OEM Mopar unit (safest) or an NGK or NKK manufacturer in order to maintain the delicate balance of what's looked for in the circuit (by the PCM). A sensor with an out-of-spec impedance often looks like an 02 sensor that's already heated to the PCM, which then tapers off its feed to the sensor, leaving it cold. Yeah, it's still broken.
Without an actual 02 sensor heater circuit... WITH a code for high voltage and running rich... I'd give the probability of a bad upstream 02 sensor about 90% chance of fixing the whole she-bang.
Let me know what you find and if you have any questions or problems. I'll be glad to help.
Thanks for writing!