I will try to add specific make/model information when I can. I personally an not an overly handy person in regards to a furnace. Uncle is hvac cert. but he's unable to figure out the problem. But can do the work if we can narrow down our issue.

Already replaced the thermal couple. The main burners will light when you turn up the t-stat. they burn strong for 45 seconds or so then everything shuts off. I assume its some sort of fault because of the way it shuts off (even blows out the pilot light) blower/fan never turns on.

This is a furnace in a house I purchased that has sat empty for nearly 6 years. So there was plenty of dirt, grime and lots of time sitting. We tried a 4 wire limit switch that uncle had laying around and replaced the 3 wire limit switch that was on the furnace. Now we don't know for sure one way or another if either limit switch was any good but the furnace did the same thing with both the old 3 wire and the 4 wire limit switch.

Much of what I've read seems to lead back to the thermal couple, but we already replaced that. So then some suggestions of some sort of bad ground is causing the fault. No idea, can't really afford to just go replacing part after part hoping to fix the issue. Any advice would be awesome! Thanks

Observe the pilot when the main burners light. If it gets too small it won't keep enough heat on the thermocouple thus causing the gas valve to shut down.