My 1998 is leeking from some ware in the back of motor, cannot find, is running hot, any suggestions

 

Did you just change the fluids and make a mess? Hose off the area where you suspect a leak and try to follow a seaping trail. Could be a broken hose to the core. A fitting broke/came loose. Or worse the head gasket went. Check your engine oil for water.

 

Go to AutoZone and borrow the Radiator Pressure tester. It is basically a small hand held tire pump with a radiator cap on it. With your engine turned OFF and COOL, attach the pressure tester to the radiator and pump it up until you reach the pressure rating of the cap. Then have a flash light handy to start looking for leaks under and around the engine.

I 've read that the Dexcool coolant can eat the lower intake gasket

 

Most likely spot is off the intake manifold. This is serious, since the dexcool has a history of destroying the intake maniford gasket. Then the air that gets in causes the dexcool to sludge up and rust the engine block. A thorough fix is to remove the intake manifolds and replace the gaskets, about $900. Meanwhile, a cheap fix is to put Bar's Leaks in the radiator.

Running hot already is a bad sign, since it sounds like it has already sludged up. The standard GM response is a pressure flush, although results are mixed.