94 PSD fuel economy drop

[999renville]

OK 94 PSD OBS Automatic 1T dually.

Fuel economy just dropped from about 17mpg hand calc to 13.14.

Supposed to leave for a vacation today! 2600 miles round trip so a few mpg is a big deal at $4/per gallon.
Idle does not seem too rough like I have a clogged injector but last time I didn't notice until two were clogged. Also power does seem a little down and not using an oil.

My question is: Is there a tester avail or a home method to do the injector test without having to pay the $85 the local guy charges just to scan. I don't mind spending a few $$$ on a tester but not the $1500 for the snap on setup.

[vitalidle]

Not sure the cheapest one I know off is the autoenginuity that will run on a pc laptop for $300 plus bones.

[999renville]

went ahead looking for low hanging fruit and changed the fuel filter. idle is a LOT quieter now. drives easier at freeway speeds. will need to check mileage but helped one problem. filter was quite dark with crud. changed only 7500 miles ago.
Seems like I've had to change the fuel filter a bit more than I should. I like to do them at 10k. Truck has 190k on it. NOT using bio-D.