Hi xxEddie, looks like it could be a grounding issue, maybe. Have a friend whom had issues with his blazer for two years. He was older and didnt want to go deep on a repair. He took the truck to the dealer. After ten days of headaches at the dealer they took the entire dash out and found the big/main wire bundle where it comes close to or through the steering column brace-formed metal frame work had worn through the wire insulation and the resulting intermittant arcing was makeing big trouble.The repair was expensive and he was disgusted with the truck problems. Sold it. I would never have guessed that one.

Aftermarket fuel pumps have a list of problems depending on the manufacturer. Everything from insufficient maximum output pressure, to leaky check valves, to noisy bearings, crappy electrical connections, short life span, low volume output, to name a few ;) AC Delco & Delphi pumps are nearly identical, in fact, I've heard they come off the same assembly line. They rarely fail with less than 100K miles. Aftermarket... I've seen them fail right out of the box, and rarely make it to 100K. I will not install aftermarket pumps on a 4.3L CSFI system, even if the customer supplies it.

As for plugs, several members use NGK and have good luck with them. I don't count on luck, I use AC Delco 41-993 with a gap of .060" (that's what came in it when it was new).

So, I've replaced the vehicle speed sensor, ignition control module, and coil.. Problem still there, but not as bad.. 3rd gear is still jumpy a bit..

Did you check fuel pressure and leakdown?
Did you replace the distributor cap & rotor with AC Delco parts?

No, I haven't been able to check it, was scared to drive it off cause the gears after 2nd were being stupid.. and I haven't touched the distributor or rotor yet.

If the engine runs poorly, the transmission will shift poorly. A transmission is similar to a computer: If you put bad information into it, you'll get bad information out of it;)

Well, after I replaced these last few parts, It runs a lot better.. Just seems like 3rd gear is slipping a little bit..

I have an airtex pump in my 97 blazer for 6plus years not a problem, guess it's the luck of the draw with any part you buy, regardless of manufacturer! I would try replacing the complete distributor, can get them for $52 on ebay shipped from Skip White, better made than factory with aluminum housing & brass terminals, plus 5 yr warranty! Good Luck!

Local Chevy dealership pulled 4 codes.. MAF, EVAP, EGR, and throttle pedal sensor.. which I've never heard of.. I replaced maf with one from pick and pull.. now it acts funny if I take off slow..

#1 Check fuel pressure and leakdown, and post the results.
#2 Find out exactly what DTC's are in memory and post them.

Some vehicles have a "throttle pedal sensor", yours does not. Yours has a throttle position sensor. If the dealer doesn't know that, find a new dealer ;)