98 F150 w/4.6 has been setting and eventually clearing itself the P0153 code for a month or so.
Now for the 1st time it set a P1151.

Are they related and possibly the same cause?

 

Read this

https://www.obd-codes.com/p0153

and this

https://www.obd-codes.com/p1151-ford

 

Bank 2 Sensor 1 - I'd replace the driver's side upstream O2 sensor.

 

I'd suggest replacing both up stream O2 sensors. If one is bad, the other one is going to puke right behind it. Changing O2 sensors should be on the 100,000 mile maintenance list. You'll get better fuel mileage using new units. DO NOT buy cheap units. Use ONLY Motorcraft sensors or expect issues. Shop around for best pricing. I get mine at Rockauto. There is a HUGE difference in the allowable operating range of the different brands. DO NOT use Bosch brand as they are a narrow band sensor and you WILL have problems.
FWIW, the downstream sensors are there just to monitor cat efficiency. They pretty much are along for the ride and are not usually a problem.

 

Thanks for the replys and heads up. Couldn't find any vacuum leaks and the engine idles & runs fine so I ordered 2ea Motorcraft 02 Sensors from Rock Auto. Looks like I can access both upstreams through the fender wells.

 

While you are doing the job, make sure the O2 sensor wires aren't chafed or resting on anything.

 

Followup, I replaced the upstream 02 sensor on the drivers side, bank 2 sensor 1, with a Motorcraft 02 sensor and this cleared my error codes and corrected the slow 02 response and lean condition.
It's run clean for over three weeks. I haven't gone through a full tank of gas yet so I don't know if my mpg is any better.

I did order another for the bank 1 sensor 1 (passenger) side but haven't swapped it out yet. The hard to get at wiring plug coupled with the sensor not wanting to break loose easily contributed to that. So I decided to wait to cross that bridge when forced to deal with it LOL.

Since the truck was running so good I took it to a friend and had him detail it, he did a great job.

 

Yeahhh buddy! Looks mean and clean! Even though I don't have those codes... I am going to change out my O2 sensors. My spark plug change had indications of running lean. A slight white crust on the plugs. Anyhow, glad your tuck is running well.