1999 GMC Jimmy Questions

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fairly new radiator, new thermostat, full of antifreeze
Who ever did the tune up last ended up cross threading the spark plug cylinder. Trying to find a tap big enough but need to know the pitch
Anytime I drive, it does not seem to hold gas in the tank. It always seems I have to keep going to the gas station. I'm not sure if my fuel pump is causing the problem
When I turn the wheel to the left, I hear a knocking sound that seems to come from the front wheel.
I do not think its the brake pads. it does not sound like a grinding noise
I also hear a thumping noise when driving like a broken belt in one of the tires, but was told that it might be the wheel bearings.
My trans is fairly new rebuild .It is slipping and the speedometer bounces up and down and some times dont work .I can manual shift in 1st and 2nd but no 3rd or overxrive .I was told it may be a vss .Vehicle speed sensor .If u can please give me ur opinion which will greatly appreaciated.Thanks Ken
Just put speed sensors in transfer case, already . it went in for probs. W/ Jimmy not selecting w/ 4wd or2wd ID like
Then it would self cancel and after a while of clicking , would shut down and service 4wd would light up on dashboard
Just did full tune up . gas gauge hasn't worked for a year. Issue w/ bucking and nearly stalling,was mostly eliminated. But was the root cause , of my fuel pump exchange. Still no gauge . did coil.tps as well
Pimp pressure of old pump was holding near 50 psi. Borderline I thought..any volt readings I should know ? Maybe test at relay? Help.

Hello, I am at my wits end tearing my hair out over this. Been a mechanic for quite a few years now but i cant seem to figure this one out. Its my personal vehicle and time is limited to get it finished.
I have a 1999 GMC Jimmy 4.3
It has come a long ways since i first purchased it but theres something left i cant seem to figure out on my own. It didnt run when i got it, however with alot of work its going now.
So far i have replaced:
-Spark plugs and wires. (Plugs AC Delco / Wires i believe are house brand since they were out of the ACDelco brand wires)
- Cap and rotor (both AC Delco)
- Fuel pump
- PCV valve
- Intake Airtemp Sensor
- Catalytic Converter
- Water pump
- Cleaned the MAF very well and it works properly.
- Few other things...
I will note that when i got it, it had a blown head gasket. However i fixed that with two seperate rounds of Blue Devil Head Gasket sealer. One time to fix it, and the second time just to be sure.

Problem is that i cant get it registered because i cant get the check engine light to go off. only thing left that comes up varies. Sometimes its either a P0300 (multiple cyl mifsire), or a P0302 (Cyl #2 misfire). But never at the same time, its always one or the other.
The Check engine light stays on solid, but then when i get up to around 30 to 40 mph the light will start flashing. I am leaning towards it possibly being the Spider fuel injector malfunctioning? Besides that the damn thing runs perfect and you ould never know anything was wrong!
Any help or input would be much appreciated thank you!
I replaced the fuel filter and pump 8 months ago. I replaced the plugs and wires 3 months ago. PCV and EGR recently replaced. Today I installed the spider injector assembly. The truck still acts like it is fighting for fuel. It stalled out on me while driving and idling. When I have been able to rev it up, it sounds strong, but when put in gear it is sluggish. I also replaced the fuel filter again today thinking that it must have been dirty. I also noticed condensation in the throttle body. I'm stumped and going broke trying to find the problem. Any advice?
Weather related? Began after an intense, Ohio Spring downfall. It hasn't rained in a few days and it is still running rough.
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