Wth the '01 I believe you should have a shrader valve on the VP. There are a few places that make test gauges that mount right to the shrader vavle. But those are only temporary hand helds ( still better than nothing though ).
Or you can decor the shrader valve and you now have yourself a 1/8 " fitting, for a full time gauge that you can mount in the cab.
IMHO, the best place to monitor your pressure is right at the VP. Then there is no guess for pressure loss through the filter or any other fittings. I run a mechanical full time gauge, mounted with a pod on the steering column. I don't use an isolater, just diesel to the rear of the gauge.
You should also definately check in to upgrading you stock fuel lines. There are many ways to do this.
Jeff