Originally started with a p0302 code, and it cleared. CEL came back on with codes p1131 and P0401. First time with an 8 plug 4 cylinder. Truck has 263000 miles, and still original (metal) DPFE sensor. Trying to avoid having to get a $80 part.

 

Welcome to FTE.
Good idea to have scanned & posted up your trouble code Numbers.
You may have more than one problem, so lets think about this some more with what the code clues may be suggesting.
Since these codes seem to have come about suddenly & the P1131 is a code for the O2 sensor lack of switching & its stuck lean, suggesting a vacuum leak & with the EGR code P0401, EGR flow insufficient detected & seeing as how the EGR valve is vacuum controlled, it might be indicating a vacuum leak in the EGR control system, like a loose vacuum line, or maybe the EGR computer controlled vacuum switching valve diaphragm is leaking & the valve isn't opening like it should & is applying a wimpy control vacuum to the EGR valve diaphragm, causing it to not open enough. or the vacuum control line between the two is corrupt. EDIT: Or maybe you have a corrupt vacuum line between the DPFE sensor & its vacuum source. A lean mixture can cause cylinder misfire, ie the P0302 code.
So, I'd begin an inspection & test of the EGR system & its vacuum plumbing, before condemning the DPFE sensor. If you do find the DPFE sensor to be at the top of your suspect list, give it a test before replacing. There is a test procedure for it in the "Tech Info" thread atop the forum thread index page. If the DPFE tests faulty, look on line for autoparts store discount codes. There are codes that range from 20-50% I've recently used, depending on how much we spend.
Some thoughts for consideration, let us know how your trouble shoot goes.