Hoping someone has an idea about what could be going on. I’ve only had the truck for a year, and noticed the same issue but it seems to be getting worse. I don’t know a lot about engines but have been trying to learn along the way

Consistently:
-a little rough to start
-does not accelerate very quickly, especially struggles 45-65mph
-when trying to go +45 up an incline it majorly struggles, and usually the CEL will flash until back on a flat surface and will turn off
-have had the codes read after this and it’s a “cylinder 4 misfire”
**this happens less if I am in overdrive

lately, this has been happening but now there seems to be no oil in the engine, or very little. 3 days ago my oil gauge was bouncing all over the place on the dash. I checked the level and put two quarts of oil, two days later checked (after not driving it) it because having the same issue and below minimum level on the dipstick. I’m still +1000 miles till my next regular oil change.
Had the codes read again and was given: P0171 code “Bank 1 system too lean”. The mechanic who gave it a quick look said there is a small oil leak but didn’t think that would be contributing to that big of an issue.

Within the last year this vehicle has had new spark plugs, wires, exhaust repair, sensor replacement, manifold gaskets, PCV valve, serpentine belt and compressor, battery, terminals, and alternator done.

I plan on taking it in to a different mechanic than I have been in the past, but am open to any ideas about troubleshooting in the meantime!

 

Welcome to the forum

There is no "smoking gun" with the info provided

Mechanic should test fuel pressure holding engine at 2,500rpms to see if its dropping, in 2003 its expected to stay above 55psi at any RPM
I would change the fuel filter, needs to be done every 5 to 7 years, it can cause lower fuel pressure at high demand, i.e. above 45mph

Flashing CEL means BACK OFF the throttle or engine damage may occur, so keep that in mind

Lean code Bank 1, means computer is having to add more fuel to passenger side cylinder to keep O2 sensor in proper range, doesn't mean engine is actually running Lean
But it does mean there is a problem

"New sensors"???
Like what, there are a few, lol

O2 sensors need to be changed every 100k miles or 12 years which ever comes first, these are the ONLY sensors that wear out

Anytime you have a misfire code you should do a compression test on all 6 cylinders
Just to rule out lower compression so you don't waste time and money on non-fixes if it is a compression issue

 

All super helpful thank you!