sounds like a leak. get yourself anohter gasket and swap it out.
Ditto.
If the gasket isn't sealing you'll get what you're having. Here's a hint. The exhaust flange where the gasket sits is usually warped from the welding process at the factory. You need to sand/grind the flange flat to make a good gasket surface.
Remove the pipe from the engine. Clean the gasket surface so there is no old gasket material then 'paint' that surface with magic marker, or machinist dye, even a light coat of paint will work. Now run that surface over sandpaper placed on a known flat surface such as glass. Just a few swipes will do. You'll quickly see where the high and low spots are. Eliminate them. They are what cause a bad sealing surface. You can tighten the fasteners all you want but if the gasket surfaces aren't flush it will eventually leak.
Make a new gasket from gasket material made for exhaust applications. I like 1/8" minimum thickness. Tighten the fasteners then check them again after a couple of heat/cool cycles. Torque is about 60 inch pounds. Good luck.
Tom
