Injectors may be the next logical step.

there's a post somewhere on here where you can take them out and make your own pressurized cleaner with a few simple parts from Home Depot , a Schraeder valve, and a compressor or compressed air tank.

Someone also posted using BG 44k to thoroughly clean the injectors, you'll find it on here.

As the injector ages the spray pattern fails, the injector dosen't close all the time -- and others. The spray pattern should be atomizing not a laser line of gas.

There are companies that will do "in car" cleaning of injectors for like $25 per injector and that includes backflushing of the fuel rails.

Just some ideas.