Odd vibration

[Owengun]

So I have a 03 Silverado 1500 with the 4.3 v6 and about 204k miles. Bought the truck a few months back with pretty much no issues other than cosmetics. Here’s where the problem comes in. Last week I drive it to and from work with no issues till I got to Thursday. Wednesday night I took it on a longer than normal drive about 70-80 miles round trip. Sat in a bit of traffic but nothing out of the ordinary. Went out Thursday morning to run to the parts store for another project and it took quite a bit of cranking to get it started. 
 

once it finally started the rpm’s stayed real low for a few seconds then jumped up to normal idle but with a significant vibration which went away as soon as it went into gear. 
 

i finish up at the parts store and go to leave and it does the same thing cranks for a bit and then finally starts with the low rpm’s then right up to normal idle still with this weird vibration. I check it out and it looks like the crank pulley with the harmonic balancer is wobbling. I limp it back to the girlfriends house and finish up what I was doing. I go to head home and it does the same thing again only it has a bad vibration when it comes back down to idle every stop light or stop sign. 
 

i got and installed a new harmonic balancer thinking that’s what it was and it helped a little so the vibration isn’t as bad but it’s still there. I also tried a new belt and that helped a little since the old one was stretched out pretty good.

 

Now taking it to work this morning it did the same thing it was before but the idle vibration is slightly better. However unlike before I’m getting the vibration all the time like one of the pulleys Is bent or something. I also noticed that it took significantly longer to shift into overdrive going down the main road compared to what it used to do. 
 

I should also mention it’s not throwing any codes or anything similar. I also know it’s not a tire or wheel issue because it does it in park as well. I can visually see the engine moving on the mounts but it doesn’t seem to be moving anymore than what would be expected for something with 204k miles. The only difference is this is a constant vibration unlike a bad motor mount. 
 

my next plan of action is cleaning the throttle body, MAF, replacing the spark plugs, and the air filter. I may also run some injector cleaner through just to see if maybe it helps but like I said I feel like it’s a wobble in a pulley or something like that not a engine running issue. 
 

Any help or anyone who has dealt with this before is greatly appreciated. 
 

update- I replaced the tensioner pulley and crank pulley on the harmonic balancer to no avail. 
 

im still stumped on this one thinking that maybe it might have something to do with the front main seal possibly. 

Edited September 5, 2022 by Owengun

[richard wysong]

sounds like maybe the torque converter is on its way out. try disconnecting it and see if the vibe goes away