I have a 1994 GMMC suburban 4X4 with a 5.7 l (350 ) v8 engine, I had to replace the engine because of a broken rist pin. Ever since the rebuilt engine has been installed it has been a real Gas consumer. Recently I pulled a boat for several hours, I noticed a great deal of unburned fuel residue on the hull of the boat. The catalic converter is running very hot. I am wondering if my bad fule consumption is the result of the fuel not being properly burned. The rebuilt engine has never performed like the old engine, Idles rough. I have replaced the "Throtle Position Sensor" and the "Anti Knock Sensor" I have tough of replacing the TBI, but I don't just want to keep shooting in the dark!! Does anyone have any ideas what is going on????

Have you checked/changed the O2 sensor?

Check your charging system too. Too weak of a charging system will
give your engine a weak spark, and leave much unburnt fuel to burn off in the cat, which is dangerous.

I wouldn't do anymore towing, and as little driving with your rig until you can get this worked out.

Best of Luck!