Apply a vacuum gage somewhere between the lift pump and the 'racor' filter(s). Most racor filters already have a gage port to do this.

Start the engine and watch the gage during constant rpm normal operation. Trial 'should' be at 80% of maximum engine rpm, with normal LOAD (prop turning) on the engine.

If the engine then stalls and the vacuum reading *increases* there IS a fuel restriction such as collapsed filter, totally 'completed' filter, obstruction on the 'diptube' (blocked screen on the dip tube), kinked fuel delivery tube, etc. etc.
If the engine stalls and there is *no increase of vacuum* (gage stays steady) then look for blocked water injection nozzle, in the exhaust system, blocked exhaust system, etc.
If the engine stalls and there is a *DROP of vacuum* ... you have an air leak in the fuel delivery system: pin hole in the lift pump diaphragm, loose compression fitting, etc.

BTW
To correctly monitor the RACOR filter(s) via use of a vacuum gage, go to http://www.parker.com/portal/site/PARKER/menuitem.7100150cebe5bbc2d6806710237ad1ca/?vgnextoid=f5c9b5bbec622110VgnVCM10000032a71dacRCRD&vgnextfmt=EN&vgnextdiv=&vgnextcatid=7364225&vgnextcat=DIESEL+FUEL+FILTRATION&Wtky=FILTERS, choose the appropriate filter type .... and find the proper technical FLOW CURVE for your specific filter.
You are looking for a graph that lists Gallon Per Minute/hour VERSUS 'differential pressure (vacuum)' psid.
You change the racor when the indicated vacuum, with the engine running at 80% of wide open throttle (WOT), is at 80% or rated maximum flow demand of YOUR ENGINE ... so you have to look up the specific engine data for the expected flow, etc.