Missing Engine

I have a 1986 98 with the 3800 Engine. The car has been driven on short runs and is not driven often. The engine has developed a low RPM miss that I have not been able to get diagnosed. It happens primarily at low RPM levels, especially in overdrive on hills at 45 MPH, and at idle. I have had spark plug wires replaced, an injector replaced, EGR and solenoid replaced. I have had the fuel pressure checked and it is ok. The spark plugs have been checked and they are ok. I understand this engine is prone to fuel-delivery problems. Also, I have had the transmission checked and there is no problem. Any thoughts on where to look next?????

You have to start somewhere & I'd start with the ignition. Get someone to assist you & start it, put it in gear & load it, bringing the RPM up to 1500-1800
or so & spray the wires & coil pack down with water, from a spray bottle. Did it act up & start to miss ? from where ? Look for bad wires, some replacements can be worse than what you took off,
use A/C DELCO. Check the coil pack or coil assy,
there are two different systems used{magnavox & a/c delco} ohm if necessary. Still nothing, if you can get it to act up, start buy using a test light & ground out one cylinder at a time untill you find the
one thats acting up. You should be able to verify if
you have good spark to it, if you do look for a fuel
problem, if not a wire/coil problem. If you have the delco coil assy you can easily swap coil positions & see if your problem follows it. If its fuel related you
might want to buy a noid light & check for inj pulse
at the questionable cyl, hopefully you have pulse &
from there I'd do an ohm check both cold & hot for
another failed inj. As far as a fuel delivery problem on this particular vehicle, thats what you say when you cant fix your customers car, is'nt it?

Same thing happened to me and i had it in a shop for a week on a dyno machine. They ended up finding out that it was a fuel injector, had all changed out and problem gone.