98 STX 4.2 codes 401, and 1132 are showing up. I have cleaned the throttle body, and maf. I just pulled the egr, and it's pretty clean with no blockages in it, or the manifold. I can clear the codes, and 401 can show up again in a few miles, or it can go for quite a few and not show up. The 1132 doesn't show up all the time, but is getting more frequent. Also, while leaving a stop, and at 1500-1800 rpm the truck will stumble lightly. Does it worse while going up a grade, and a little worse again while pulling a trailer. Any ideas?

 

Here is another case of not paying attention to what the codes are telling you. The tipoff is the 1132 code for bank 1 front.
It says the bank 1 front OX sensor no longer sees the sensor switching in response to exhaust content changes.
Suggest an air leak in the intake at some point making that bank lean.
So it comes and goes being marginal.
The 401 code may or may not be associated with the 1132 code because it is a seperate function.
If the EGR is leaking exhaust into the intake it could be a reason for the 1132 but you would see rough idle and running with that leak.
401 code is low flow, not a leak.
Test the EGR valve for operation with the engine at idle by applying a small amount of vacuum to it through it's hose.
If the engine responds with rough idle, chances are that part of the sytem is clear.
If it does not, there is a blockage at some point.
The DPFE can be the source of failure if it cannot report the result for flow testing.
The EVR gates vacuum to the EGR. If it has an issue not passing vacuum, low flow code is the result.
Good luck.