I have 98 yukon 5.7. I just had a diagnostic ran on it and was told that I need to replace the catalytic converter. It is a y shaped double converter. They sell a direct and a universal fit. What I want to know is with a direct fit does it just bolt on without any mods? Will I need anything else to ad when replacing? I figure if I can do it myself I can save a
Good bit of money verses paying for it.

Well, direct fit should mean direct fit. Of course, that may vary from manufacturer to manufacturer, but a reputable product from a reputable company should be a true direct fit.

I recently replaced my catalytic converter with a Random Technology direct fit converter, and it was a true bolt-on. I simply removed my O2 sensors from the OEM converter, plugged them into the new converter, and bolted it up.

Considering you have a '98, you may have some difficulty removing the original converter. I spent a LOT of time separating my OEM converter from the remainder of the exhaust aft of the converter. The three nuts at the converter were so corroded they barely resembled nuts. I removed the entire exhaust, breaking the rear spring bolts in the process, and necessitating replacing the entire exhaust. Since I had ruined the "catback" portion of the exhaust, I hacksawed it close to the converter and took the converter to a buddy with a shop. He had to grind the nuts off.

The bolts holding the converter to the exhaust manifold were no problem, but results vary from vehicle to vehicle. My car is an '02 Acura RSX, with 77K Michigan miles, just for reference.

Thanks for the info. I figure that's how it should be but wanted to be sure before I went and bought it and possibly ended up stuck needed to get it to a shop. Needless to say I am not alone in wanting to do a job myself instead of taking it to a shop for what they will charge.

You may well end up taking it to a shop, depending on your skill and tool level...