99 5.3 random misfire

[bearhead]

hey yall, i havent searched in thru the forum yet figured id ask then look

 

99 gmc 5.3, that has a random misfire, new plugs, wires look new as well, i added some fuel injector cleaner the other day and the light came on, added another botttle and the check light went off, whelp, it came back on today, all randoms, seems to come on at 65+ speeds, any thoughst?

[oldscsc]

Check fuel pressure at the Schraeder valve. Should be 55-62 PSI with the key on and engine off.

[bearhead]

havent gotten to the pressure yet but heres a wierd sympton, the light goes off after a while, until the truck in driving down an incline, its come on 5 days in a row at the exact same spot. fuel filter?

[anumber1]

havent gotten to the pressure yet but heres a wierd sympton, the light goes off after a while, until the truck in driving down an incline, its come on 5 days in a row at the exact same spot. fuel filter?

If you check the fuel pressure, you can possibly narrow down if it's a fuel issue or not.

[bearhead]

transmission rebuild fixed issue

[Celerity]

Oh man, I didn't want to hear this.

 

My 03 is doing the same thing. It's not misfiring - fuel is fine and the transmission shifts smooth as glass.  But when it's in overdrive, going up an incline (even slight) it will skip.  Downshift and it's fine.  I'm tracking things down to a trans issue, but everyone else is urging me to replace all of the coils, plugs and wires.

 

I don't think that's the issue. I have no CEL whatsoever.