'94 Burb timing question

[Leftyarmstrong]

Got this "free" 3/4 ton, 4wd Burb with a 454 (trans?). When I went to pick it up in the California desert, it started right up even though it's been sitting for years. Runs real strong. Hauls ass for a big heavy. Anyways, took it in for pre-smog and they said it needed an O2 sensor and cat. Did that. Failed smog for NO. Took it back to pre-smog guys and two days later they said the harmonic balancer slipped so it won't time. Brought it home and put on a new balancer. Made no difference and I don't think the old balancer had slipped. The timing mark was way advance of the tab by several inches. When I try to set the timing at 4 degrees, it barely runs. What is up with this thing? Would it run at all if the timing chain had slipped? Would a stretched chain do this? Engine is original and other than maintenance, nothing has been done to it I don't think. I've spent $720 paying the back registration and I now have more money into this "free" vehicle than its worth but I thought it would make a good donor for a re-body with a pre-smog Burb. Until I find that vehicle, want to register and drive this thing as it would make a very good tow vehicle. Thanks, Don in So Cal.