Hello valued Ranger experts.

I am a wheelchair driver. I have a 98 ranger XLT 4.0. 300,000 miles and going strong. Regular maintenance.
My check engine light has been on for over 10 years. Running solid with check engine light on.
Retired with limited income. It is my only independent transportation. I need it to have quality of life. I reside in an assisted living facility.
Decided to address problem.
Codes PO171 and PO174 too lean. I have changed intake manifold gaskets, valve cover gaskets, MAF and all 3 o2 sensors. EGR, Idle control, and PCV valves. Fuel pump, power steering pump, NGK plugs and wires, and oil change. Mechanic checked for vacuum leaks and found none. Drove, and check engine light came back on after 17 miles. Any ideas?
Was told maybe check engine light ingrained in computer and to drive for 2 hundred miles. I am very frustrated and can't afford a new or used vehicle. No dents, and Betsy is still running strong. Too lean code keeps coming back on read out. If you have time, could you please advise.

My Betsy.
Mechanic taking my limbs already. You are my last hope. Thanks for any suggestions you may have. After downstream o2 and EGR change rough idle. Idle relearn is what needs to be done now. Check engine light going to bankrupt me. HELP!!!