1994 Nissan Maxima Repeated Fuel Injector Problems

I drive a 1994 nissan maxima, with the 3.0L VG30DE SOHC V-6 engine. About 15,000 miles ago, I had to replace one of the fuel injectors (the injector circuit was open). Then about 10,000 miles ago, the same problem occured, but with a different injector. Since it is so much work to get to the injectors to replace them, I replaced all remaining injectors at the same time. Today, (10,000 miles later) the same problem occured: an open circuit in the #5 cylinder injector. From what my maintenance manual says, the injector resistance should be between 10-14 ohms. The rest test within this range.
Why would I be having so many problems with the injectors? Is there something wrong the the PCU that keeps creating this problem? Would a clogged injector (caused by not changing fuel filter often enough) cause an injector to read open on a resistance check?
This is getting frusterating, and I would like to get to the root of the problem before I change injectors again.