What brand of cap and rotor did you use? These engines are extremely picky when it comes to ignition parts, especially the cap and rotor. I generally recommend the best you can afford, with ACDelco if at all possible. I've seen the cheaper units, including some of the bigger national brands, miss right out of the box. It would be a good idea to check the dist drive gear as they do have a tendency to knife edge over time, even at your mileage. If you do pull it, be aware that you need a scanner that can run the GM cam sync test to set the timing. It has to be set at 0 plus or minus 2 degrees, and can be easily gotten out of adjustment even if you've marked and realigned it well. If the ignition checks out, the fuel system is the next major caveat of the Vortecs. Check that KOEO fuel pressure is over 60 psi and KOER pressure is no less than 55 psi. With ot running, bring the rpm's up and ensure that it doesn't drop out of spec. If all is well, check that the system is holding pressure by cycling the key a few times, then turning it off. If it falls quickly to zero, you have an issue. Clamp off the return line (it's stainless braided rubber behind the engine) and repeat the test. If it doesn't drop, your regulator is faulty. If it does, check deadhead pressure by pulling the line off the fuel filter and adapting the gauge to it (you can use FI rated fuel hose and clamps). You should have 80 to 90 psi, and with the key off it should not drop. If it does, your pump is getting loose and should be replaced. If deadhead is good, and you have a drop even with the return plugged, the it's either the regulator or a leaking injector poppet, both of which the Vortecs are infamous for. Recommendation here is to get the upgraded Delphi MPFI spider and replace everything. It costs around 267 plus gaskets. If that's out of the budget, remove the upper intake leaving the spider in place. Pull all of the poppets out of their holes in the intake, reconnect the fuel lines, and turn the key to the run position. Looks for drips. If you don't see one immediately, cycle the key a few times. You should see a fuel leak at the offending injector, or from the regulator. Replace the defective units and roll on. Hope this helps.
