Need ideas, 98 vortec 5.7 irratic timing advance

[Vortec1]

Hey, I've got a 98 chevy k1500 4x4 with the vortec 5.7. Recently I've been battling a stumble on acceleration. I've done the basic tune up stuff, cap,rotor,wires,plugs,fuel filter, maf,map & iat.
I recently purchased an Ultragauge (kind if like a scanner with live info) during acceleration I'm getting random jumps in timing advance, under steady throttle I can see up to 35° advance and 10° moments later correlating with the stumbling of the motor. I've seen up to 40° advance and -0.5 retarded just cruising around the city...
I have 1 current trouble code P0440 but thats been there long before this issue began.. Anyone have any suggestions on where I might look next? Could this be a distributor issue or possibly a crank sensor on its way out? Any ideas are appreciated. Cheers!
Just rolled 255000km

 

[JOHNGAAA1]

You need a new distributor assembly. Its worn out. The distributor is "WALKING".

 

[Vortec1]

Thanks! Is there anything I can check out visually to confirm? Not in the greatest financial position at the moment.. hoping I make it to work tomorrow

 

[Schurkey]

Is the timing advance abnormalities the CAUSE of the stumbling, or a RESULT of the stumbling?

True enough, Vortec distributors have a poor reputation for longevity. The distributor gears wear, as do the bushings within the plastic distributor housing--then the shaft wobbles around.

 

[Vortec1]

Is the timing advance abnormalities the CAUSE of the stumbling, or a RESULT of the stumbling?

True enough, Vortec distributors have a poor reputation for longevity. The distributor gears wear, as do the bushings within the plastic distributor housing--then the shaft wobbles around.

Thats what im unsure about. I understand intake gasket leaks are also common on these trucks, I've tried using propane around the intake to get a rise out of it but no dice. It doesn't only seem to be related to being under load now, even light load stop & go traffic it stumbles now... No fluctuation at idle that I can see, sits around 23ish degrees pretty steady. Recently replaced the throttle body gasket but I double checked and it's buttoned down tight and seated in the correct groove

 

[bowtie539]

Hey vortec1, I'm in a similar position you are. I have a 98 2500 with the 5.7 that I inherited after a friend passed. After replacing a bad fuel pump it had been running fine for the passed year. Now it is doing exactly what you had described. At idle I'm hovering between 22.5°-24° of timing advance for #1 cylinder. However when I start driving I get stumbling and hesitation almost like feels like a bad coil pack. Just curious if you have solved your problem. Any help always appreciated. Thanks