First off sorry if this is answered somewhere I'm not sure what exactly to search for.

2000 LS, 4.3 L, 3 button 4WD switch, 2 door.

Ok so yesterday my truck started having some sort of power or fuel supply issue. When I'm going from idle/low speed and speeding up, I lose power for half a second, all gauges drop and acceleration drops then comes back up. It's like when you run out of gas or your fuel pump dies, but only for a second. Once I get up to speed and it 'warms up' after about 10 km the problem seems to go away.
Today when I started it to leave work, it literally lunged forward like it was getting a ton of power, much more noticeable than a normal start.

Background:
At the beginning of summer I replaced my fuel pump (after trying 3, they finally upgraded the brand and sent me one that works). Since then, if I fill up gas until the pump stops itself, gas will splash out somewhere above the tank (not at the fuel pump, everything is dry at the connections). I'm pretty sure my evap system is screwed and plan on replacing the cannister, purge valve (square one) in front of tank and the solenoid at the engine.
Could the evap problem cause this? Where should I start to look?
Also, I bought a new gas filter (in case I got rust in the tank when changing the pump) but the nut on the line was very rusted, so my dad suggested leaving it so I don't break or twist the gas line.

Is there any way to rule out the pump, or do I have to wait for it to die completely and not make any sound when i turn the key to the on position...?

Possibly stuff in the line blocking the fuel for a bit? Should I check out and clean the throttle body or EGR or something?
Replaced the plugs and wires at the end of last year.
My dad may be a mechanic, but I don't know much, I'm learning as I go - with the help of this awesome forum BTW

Other info that may be useful, i'm not sure: idles around 550 rpm stopped in drive and roughly 700 - 1000 in park.

Hopefully that's enough info for someone to have an idea
Thanks!

 

What brand of pump did you use? I would start off with a fuel pressure and leakdown test. With the key on, engine off, you pressure should be between 60 and 65 and not go below 55 for 10 minutes, post back your initial and 10 minute later numbers.

 

i agree with 50lb. but lets review. you replaced the spark plugs, with what brand??? it may seem stupid but if you used something other then AC DELCO- CHANGE THEM FIRST!!! other brands after a few miles/months will cause the engine to miss and lurch and lack power, it has happened to me and friends. next the gas spillage, check the fuel fill pipe from the fill neck to the tank,these will rust out because of how they are mounted. have had 2 blazers and both had evap codes and both had rusted out filler pipes. hope this helps.

 

Four fuel tank drops, you could have broken front vent line on tank, fuel leak.
This should not cause your current problem.
Follow 50lb with pressure test. If thats OK I would start thinking electrical, ignition switch, maybe?

 

Can i get the pressure gauge anywhere pretty much?

Update: it definately does the lurching thing in the first 3 shifts from stopped then it is fine. Also yesterday i drove all day and it didnt happen once, i put injector/carb cleaner in, but i swear it cant be that easy. Also took her in to get a U joint changed and they couldnt change the fuel filter either said ill have to cut it off and rig something.
For the filler neck; i did have trouble lining the end up so i could bolt it to the body. Mine has 2 tubes, one for venting i assume. Should i fill till it leaks and check there? Pretty sure i woulda found that tho cause i can reach it by hand

 

Sorry forgot some replies. I used ac delco for plugs and wires. Had trouble in a diff car using the expensive platinum ones. And theres no problems starting or idling. Only when i give it gas from stopped. Im thinking the purge valve by the tank is screwed and when i overfill gas goes through the vapour line into the canister and it splashes out there somewhere. When i bought a new gas cap, and so it was making a proper seal to build pressure, all i can smell is gas from the front of the truck. But there is NO leak when that happens. I really want to do the pressure test jus gotta get a gauge

 

Start with the pressure test, you can either buy one for about 40 bucks IIRC, or rent one from most parts stores.
Edit: I would find another shop if they can't even change the fuel filter, they can be a PITA when the bracket gets rusty, but they shouldn't turn you away.

 

Absolutely. Anybody who holds himself out as a pro mechanic should get that filter off correctly.

 

Becuase this sounds exactly like the problem I am having, have you noticed any other gauges bouncing when it stalls? My temp gauge bounces when the RPM gauge bounces as its stalling.

 

All of my gauges drop.

The shop didnt want to change it and rig something without my approval and i wasnt there. Its active green and ross.
BTW today on the way to work still no problems. Then on the way home about halfway it was dropping a tiny bit. But not nearly as bad.