I've never heard of those symptoms before, but you might want to make sure there is nothing wrong with the main harness; because if you get a new ECM and there is something in the harness grounding out then you will have ruined your new ECM too.
In the past when I've come across a fried ECM I was able to take it apart to expose the circut board and was able to see the burnt spot. There may be a way to track down the culpret by plugging in the circut board and removing fuses/relays or tracing heat until something is exposed.
Those old 99 harnesses are a pain, especially now that we are 12 years in. FYI a 2002-2006 TC harness is an almost direct swap in and you can benefit from the new style ECM. I just did this swap recently to a 99 if you need more info. The harness and ECM could be purchased used for less than the cost of a 99 ECM new. Plus the new system makes the old motor run a bit smoother too!
The Vic Shop, Inc