hard start/stumbles at constant speed

I hope someone can help me with my 95 blazer problems= Started out stumbling at constant speeds. Then would die on my a few times and hard to start. Finally had to have it towed to dealer. They had it about a month and changed the injector spider. Said it was going down when hot and holding pcm down. Got it back and still noticed the stumbling. Took it back and they couldn't find anything. Drove it a week or so and it was hard to start. Drove a couple more days and it wouldn't start for 3 days. Had it towed to dealer again and it started right up for them. They kept it another month trying to duplicate the hard start. They got it to do it once, but didn't have their equipment hooked up to it. So I took it home.
I've changed the coil, plug wires, distributor cap and button. It has a fairly new fuel pump and filter, 6months old. I suspect a electrical problem since they said the fuel injector was shorting out. I've checked the battery and it is ok. Next I took the negative cable off the post and used a test light between the two. The light lit. I started removing fuses that are hot all the time. I removed every fuse that had voltage. The light still lit. I checked voltage and am reading 4.2 volts between the negative cable and negative post on battery. I removed wiring from the alternator and the voltage went to 0. I had the alternator checked at autozone and they said it was ok.
My question is would this 4.2 volts concerning the alternator affect the hard starting of my blazer and the stumble at constant speeds? Can the alternator be shorting to ground and the alternator still be ok? Should I change it?
Thanks for your time!

Have you removed and cleaned the EGR valve?

Have you removed and cleaned the EGR valve?
Yes I have, but haven't had the chance to drive it yet. It wasn't plugged or stuck. I did notice that the gasket appeared to have been leaking though. Will take it for a spin this evening.

Took it for a drive and still has the stumble. Not really sure what to call it, stumble, miss, surge? at constant speed. Wasn't hard to start this time. Most of the time it starts fine. It's just those few times that worries me. I don't want to be stranded again.

I finally decided to change the computer, I thought since the shop said the injector went bad and was pulling down the computer. I thought maybe it damaged it electrically. Seemed to do ok for about a week and a half to two weeks and then it had a couple of hiccups while driving. Also, after changing the computer, it seemed that my brake pedal was easier to use (before I was wondering if there was something wrong with the brakes, I had to press harder to stop) I was traveling about 50mph and going up a grade and gave a little more gas and it jerked a couple of times. The next day it did the same thing once. Then it continued to do it but not like the hesitation it was doing before. Finally the other day I drove it about 5 miles to the bank and when I came back out and got going and came to a stop it died. I did get it restarted and took off. It seems like it would stall and restart itself. I did get back home and shut it off for a little bit. I restarted it. It had cooled off a bit. After the temperature got up to normal it started cutting out idling. I put a guage on the fuel rail and found the pressure ok and it would go up a pound or two when it would cut out. I put it in gear in the driveway and it would chug when I gave it just a small amout of throttle, forward and reverse. If I gave it more it would take off. I thought that it may have something to do with the temperature so I changed the engine coolant sensor, didn't help. Does anyone have any ideas? Does anyone have any ideas?

What is your temp gauge reading when the engine is warmed up?

1/2 1/4?

Have you had the fuel pressure checked? If the injector is not getting 55psi it will not open the poppets valves and the cylinders will not get fuel.

Also

Finally I think I've found the problem. A bare wire going to the engine coolant sensor. Taped it up and seems to be ok. I'll drive it a while to make sure. If this wasn't it, I'll make another post.