I have a 1995 S-15 Jimmy with the exact same problem. It takes about 10 seconds of cranking to get it to start and once it does it idles extremely rough. It also stinks of unburnt fuel when idling, gets about 13 Mpg and has a surging sensation when driving a steady 55-60 Mph. From the research that I have done, I came to the conclusion that it was the Fuel Pressure Regulator, but apparently the 95 and 96 4.3L Vortec 'W' either doesn't have one or it may be part of a combination unit under the plenum. I'm convinced I'm on the right track but could use some help determining whether or not this engine has a regulator or what does the same job as the regulator. I have already replaced the O2 sensor in the exhaust manifold and have changed the EGR valve.